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siRNA loading into EVs

Supplementary Figure S1 shows composition of the EVHB protein and making of EXO-DEPTS. Supplementary Figure S2 shows the size and proteins that characterize extracellular vesicles. Supplementary Figure S3 shows that the mRNA is inside the extracellular vesicles. Supplementary figure S4 shows that low doses of IVT EXO-DEPTs are ineffective. Supplementary Table S1 provides full names of abbreviations used in Figure 6.

EVHB protein sequence

Prodrugs are harmless until activated by a bacterial or viral gene product; they constitute the basis of gene-delivered prodrug therapies called GDEPT, which can kill tumors without major side effects. Previously, we utilized the prodrug CNOB (C16H7CIN2O4; not clinically tested) and enzyme HChrR6 in GDEPT to generate the drug MCHB (C16H9CIN2O2) in tumors. Extracellular vesicles (EVs) were used for directed gene delivery and HChrR6 mRNA as gene. Here, the clinical transfer of this approach is enhanced by: (i) use of CB1954 (tretazicar) for which safe human dose is established; HChrR6 can activate this prodrug. (ii) EVs delivered in vitro transcribed (IVT) HChrR6 mRNA, eliminating the potentially harmful plasmid transfection of EV producer cells we utilized previously; this has not been done before. IVT mRNA loading of EVs required several steps. Naked mRNA being unstable, we ensured its prodrug activating functionality at each step. This was not possible using tretazicar itself; we relied instead on HChrR6′s ability to convert CNOB into MCHB, whose fluorescence is easily visualizable. HChrR6 mRNA-translated product's ability to generate fluorescence from CNOB vicariously indicated its competence for tretazicar activation. (iii) Systemic IVT mRNA–loaded EVs displaying an anti-HER2 single-chain variable fragment (“IVT EXO-DEPTs”) and tretazicar caused growth arrest of human HER2+ breast cancer xenografts in athymic mice. As this occurred without injury to other tissues, absence of off-target mRNA delivery is strongly indicated. Many cancer sites are not amenable for direct gene injection, but current GDEPTs require this. In circumventing this need, a major advance in GDEPT applicability has been accomplished.

Contains 3 tables and 8 figures with legends.

EV markers Western blot

TEM images of EVs

This paper deals with specific targeting of the prodrug/enzyme regimen, CNOB/HChrR6, to treat a serious disease, namely HER2+ human breast cancer with minimal off-target toxicity. HChrR6 is an improved bacterial enzyme that converts CNOB into the cytotoxic drug MCHB. Extracellular vesicles (EV) were used for mRNA-based HchrR6 gene delivery: EVs may cause minimal immune rejection, and mRNA may be superior to DNA for gene delivery. To confine HChrR6 generation and CNOB activation to the cancer, the EVHB chimeric protein was constructed. It contains high-affinity anti-HER2 scFv antibody (ML39) and is capable of latching on to EV surface. Cells transfected with EVHB-encoding plasmid generated EVs displaying this protein (“directed EVs”). Transfection of a separate batch of cells with the new plasmid, XPort/HChrR6, generated EVs containing HChrR6 mRNA; incubation with pure EVHB enabled these to target the HER2 receptor, generating “EXO-DEPT” EVs. EXO-DEPT treatment specifically enabled HER2-overexpressing BT474 cells to convert CNOB into MCHB in actinomycin D–independent manner, showing successful and specific delivery of HChrR6 mRNA. EXO-DEPTs—but not undirected EVs—plus CNOB caused near-complete growth arrest of orthotopic BT474 xenografts in vivo, demonstrating for the first time EV-mediated delivery of functional exogenous mRNA to tumors. EXO-DEPTs may be generated from patients' own dendritic cells to evade immune rejection, and without plasmids and their potentially harmful genetic material, raising the prospect of clinical use of this regimen. This approach can be used to treat any disease overexpressing a specific marker. Mol Cancer Ther; 17(5); 1133–42. ©2018 AACR.

Methods/legend to Video 1

EVHB three-dimensional structure

Background: SB3 (trastuzumab-dttb) is a biosimilar approved globally based on its similarity with reference trastuzumab (TRZ) demonstrated by thorough comparability exercises in analytical, biological, and clinical studies. In a randomized, double-blind, multicenter Phase 3 study of 875 patients with HER2-positive early or locally advanced breast cancer in the neoadjuvant setting, equivalent efficacy, similar safety, pharmacokinetics, and immunogenicity between SB3 and TRZ were shown. However, when quality attributes of TRZ were examined, downward drifts in antibody-dependent cell-mediated cytotoxicity activities (ADCC) were observed in the TRZ lots with expiry dates ranging from Aug 2018 to Dec 2019. Some of these lots of the reference product were found to be used in the Phase 3 study. After completing the Phase 3 study, patients from select countries were included in a follow-up observational study to monitor cardiac safety and survival. Here, we report the final survival results, including post-hoc subgroup analysis based on ADCC status, at a median follow-up of 68 months. Methods: During the follow-up observational study, the protocol was amended to include additional patients who originally were enrolled in the Phase 3 study but had not been followed in the observational study, in order to collect a larger sample of survival data. For these additional patients, medical records from the last assessment in the Phase 3 study through the date of enrollment in the follow-up study were collected retrospectively. As post-hoc analysis, patients in the TRZ arm were stratified into two subgroups: patients who received during neoadjuvant treatment at least one vial of TRZ with downward drift in ADCC as “Drifted TRZ”, and the others as “Non-drifted TRZ”. Event-free survival (EFS) and overall survival (OS) were assessed. Results: Of 875 patients randomized in the Phase 3 study, 538 patients (SB3, N=267; TRZ, N=271) were enrolled in the follow-up observational study: 367 patients were initially enrolled in the follow-up study, and 171 patients were additionally enrolled following the protocol amendment. The median follow-up duration was 68 months from randomization in the Phase 3 study. 54 events (20.2%) in the SB3 arm, and 67 events (24.7%) in the TRZ arm were reported (HR 0.84 [0.58, 1.20], p=0.335). 22 deaths (8.2%) and 38 deaths (14%) were reported in SB3 and TRZ arms, respectively (HR 0.61 [0.36, 1.05], p=0.073). In post-hoc analysis, of 271 patients in TRZ arm, 107 patients were grouped as “Non-drifted TRZ”, and 164 patients as “Drifted TRZ”. 19 events (17.8%) in the Non-drifted TRZ group and 48 (29.3%) events in the Drifted TRZ group occurred (HR 2.57 [1.28, 5.14], p=0.008). 9 deaths (8.4%) in the Non-drifted TRZ group and 29 deaths (17.7%) in the Drifted TRZ group were reported (HR 3.87 [1.37, 10.93], p=0.011). No difference was observed between SB3 arm and Non-drifted TRZ group in terms of EFS (HR 1.28 [0.73, 2.22], p=0.391) and OS (HR 0.99 [0.42, 2.31], p=0.975). Conclusions: Comparable long-term efficacy results in EFS and OS were shown at 68 months of follow-up, further supporting biosimilarity of SB3 to the reference product. Currently, these follow-up results represent the longest monitoring data of patients treated with a trastuzumab biosimilar for HER2-positive early or locally advanced breast cancer. Citation Format: Xavier Pivot, Mark D Pegram, Javier Cortes, Diana Lüftner, Gary H Lyman, Giuseppe Curigliano, Igor M Bondarenko, Mikhail Dvorkin, Jin Hee Ahn, Seock-Ah Im, Maria Litwiniuk, Yaroslav V Shparyk, Gwo Fuang Ho, Nikolay V Kislov, Marek Wojtukiewicz, Tomasz Sarosiek, Yee Soo Chae, Jin Seok Ahn, Hyerin Jang, Sujung Kim, Jiwon Lee, Soo Young Lee, Ye Chan Yoon. Final survival analysis of a phase 3 study comparing SB3 (trastuzumab biosimilar) and reference trastuzumab in HER2-positive early or locally advanced breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-04.

Background: Hormone receptor-positive (HR+) is the most common molecular subtype of breast cancer accounting for approximately 2 out of every 3 patients. Adjuvant anti-estrogen therapy is the cornerstone of systemic therapy, underscoring the critical role of endocrine treatment which affects the majority of women with breast cancer. Furthering efforts to better understand endocrine response and resistance and implementing genomic tools to help individualize patient selection for endocrine therapy are of ongoing importance to improve outcomes. Breast Cancer Index (BCI) is a gene expression signature composed of the Molecular Grade Index (MGI) and HOXB13/IL17BR (H/I) that predicts the likelihood of extended endocrine benefit and quantifies the risk of both late (5-10 years) and overall (0-10 years) distant recurrence. BCI has recently been incorporated into the NCCN clinical practice guideline as a biomarker for prediction of benefit from extended endocrine therapy in patients with early-stage, HR+ breast cancer. The objective of the BCI Registry Study is to collect real-world evidence at a national level aimed at advancing patient care and optimizing duration of endocrine treatment and will be conducted in two phases. First, long-term patient outcomes and the impact of BCI on decision-making based on physician and patient reported outcomes as well as medication adherence to extended endocrine therapy will be assessed. Secondly, individual patient data on over 40 clinical variables will be collected and partnered with molecular profiling and genomic data for each patient to enable correlative analysis and novel biomarker research of endocrine sensitivity and resistance. Study Description: The BCI Registry Study is a prospective, multi-center, observational data registry and biospecimen repository for stage I-III HR+ breast cancer patients. The main objective of the Registry Study is prospective characterization of BCI predictive and prognostic performance. The primary endpoint is time to distant recurrence (TTDR), defined as the interval between the time of BCI testing and the first metastasis at distant organs. Secondary endpoints include time to any recurrences and medication adherence score over time. Eligibility criteria includes confirmed diagnosis of HR+ early-stage invasive breast carcinoma (ductal, lobular, or mixed ductal/lobular), either HER2 negative or positive and either node-negative or node-positive tumors with 1-3 positive lymph nodes (N1). Patients must have completed 4 to 7 years of primary adjuvant endocrine therapy and have pre-treatment tumor tissue available from a previous breast surgery or biopsy. Both physicians and patients will complete a pre- and post-test Decision Impact Questionnaire to assess the impact of BCI results on extended endocrine therapy decision-making. Patients who elect to complete 10 years of endocrine therapy will answer a Medication Adherence Questionnaire during annual follow-up visits. Follow-up of patients will end 10 years from initial breast cancer diagnosis. The Registry plans to enroll approximately 3,000 patients across approximately 40 study sites in the United States. Enrollment for the study began in Q2 2021, and 324 patients have been enrolled as of July 2021. For more information, please visit the ClinicalTrials.gov registration: NCT04875351. Citation Format: Joyce A O'Shaughnessy, Jenny R Fox, Carlos A Encarnación, Brandon O'Neal, Kai Treuner, Tara Sanft, Rachel C Jankowitz, Mark D Pegram, Catherine A Schnabel, Sami G Diab. The Breast Cancer Index registry study: A prospective multi-center observational study to evaluate patient outcome, clinical impact, and medication adherence in HR+ breast cancer patients considering treatment with extended endocrine therapy [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT1-10-01.

Purpose:HER2 mutations (HER2mut) induce endocrine resistance in estrogen receptor–positive (ER+) breast cancer.Patients and Methods:In this single-arm multi-cohort phase II trial, we evaluated the efficacy of neratinib plus fulvestrant in patients with ER+/HER2mut, HER2 non-amplified metastatic breast cancer (MBC) in the fulvestrant-treated (n = 24) or fulvestrant-naïve cohort (n = 11). Patients with ER-negative (ER−)/HER2mut MBC received neratinib monotherapy in an exploratory ER− cohort (n = 5).Results:The clinical benefit rate [CBR (95% confidence interval)] was 38% (18%–62%), 30% (7%–65%), and 25% (1%–81%) in the fulvestrant-treated, fulvestrant-naïve, and ER− cohorts, respectively. Adding trastuzumab at progression in 5 patients resulted in three partial responses and one stable disease ≥24 weeks. CBR appeared positively associated with lobular histology and negatively associated with HER2 L755 alterations. Acquired HER2mut were detected in 5 of 23 patients at progression.Conclusions:Neratinib and fulvestrant are active for ER+/HER2mut MBC. Our data support further evaluation of dual HER2 blockade for the treatment of HER2mut MBC.

Supplementary Figure from The Phase II MutHER Study of Neratinib Alone and in Combination with Fulvestrant in HER2-Mutated, Non-amplified Metastatic Breast Cancer

Purpose: HER2-positive breast cancer is heterogeneous. Some tumors express mutations, like activating PIK3CA mutations or reduced PTEN expression, that negatively correlate with response to HER2-targeted therapies. In this exploratory analysis, we investigated whether the efficacy of trastuzumab emtansine (T-DM1), an antibody–drug conjugate comprised of the cytotoxic agent DM1 linked to the HER2-targeted antibody trastuzumab, was correlated with the expression of specific biomarkers in the phase III EMILIA study.Experimental Design: Tumors were evaluated for HER2 (n = 866), EGFR (n = 832), and HER3 (n = 860) mRNA expression by quantitative reverse transcriptase PCR; for PTEN protein expression (n = 271) by IHC; and for PIK3CA mutations (n = 259) using a mutation detection kit. Survival outcomes were analyzed by biomarker subgroups. T-DM1 was also tested on cell lines and in breast cancer xenograft models containing PIK3CA mutations.Results: Longer progression-free survival (PFS) and overall survival (OS) were observed with T-DM1 compared with capecitabine plus lapatinib in all biomarker subgroups. PIK3CA mutations were associated with shorter median PFS (mutant vs. wild type: 4.3 vs. 6.4 months) and OS (17.3 vs. 27.8 months) in capecitabine plus lapatinib–treated patients, but not in T-DM1–treated patients (PFS, 10.9 vs. 9.8 months; OS, not reached in mutant or wild type). T-DM1 showed potent activity in cell lines and xenograft models with PIK3CA mutations.Conclusions: Although other standard HER2-directed therapies are less effective in tumors with PI3KCA mutations, T-DM1 appears to be effective in both PI3KCA-mutated and wild-type tumors. Clin Cancer Res; 22(15); 3755–63. ©2016 AACR.

Supplementary Fig 1. Overall survival by HER2 mRNA percentile Supplementary Fig 2. Patient disposition and biomarker availability in the EMILIA trial. Supplementary Fig 3. Potential mechanism by which T-DM1 may bypass a common resistance pathway in HER2-positive cancer cells Supplementary Table 1. REMARK2 Checklist. Supplementary Table 2. Selected Patient Demographic and Baseline Characteristics by Treatment Arm in Evaluable and Nonevaluable Patients.

Supplementary Table from The Phase II MutHER Study of Neratinib Alone and in Combination with Fulvestrant in HER2-Mutated, Non-amplified Metastatic Breast Cancer

Purpose:HER2 mutations (HER2mut) induce endocrine resistance in estrogen receptor–positive (ER+) breast cancer.Patients and Methods:In this single-arm multi-cohort phase II trial, we evaluated the efficacy of neratinib plus fulvestrant in patients with ER+/HER2mut, HER2 non-amplified metastatic breast cancer (MBC) in the fulvestrant-treated (n = 24) or fulvestrant-naïve cohort (n = 11). Patients with ER-negative (ER−)/HER2mut MBC received neratinib monotherapy in an exploratory ER− cohort (n = 5).Results:The clinical benefit rate [CBR (95% confidence interval)] was 38% (18%–62%), 30% (7%–65%), and 25% (1%–81%) in the fulvestrant-treated, fulvestrant-naïve, and ER− cohorts, respectively. Adding trastuzumab at progression in 5 patients resulted in three partial responses and one stable disease ≥24 weeks. CBR appeared positively associated with lobular histology and negatively associated with HER2 L755 alterations. Acquired HER2mut were detected in 5 of 23 patients at progression.Conclusions:Neratinib and fulvestrant are active for ER+/HER2mut MBC. Our data support further evaluation of dual HER2 blockade for the treatment of HER2mut MBC.

PURPOSE Effective therapies are needed for the treatment of patients with human epidermal growth factor receptor-2 (HER2)-positive metastatic breast cancer (MBC) with brain metastases. A trastuzumab radioisotope has been shown to localize in brain metastases of patients with HER2-positive MBC, and intracranial xenograft models have demonstrated a dose-dependent response to trastuzumab. METHODS In the phase II PATRICIA study (ClinicalTrials.gov identifier: NCT02536339 ), patients with HER2-positive MBC with CNS metastases and CNS progression despite prior radiotherapy received pertuzumab plus high-dose trastuzumab (6 mg/kg weekly) until CNS or systemic disease progression or unacceptable toxicity. The primary end point was confirmed objective response rate (ORR) in the CNS per Response Assessment in Neuro-Oncology Brain Metastases criteria. Secondary end points included duration of response, clinical benefit rate (complete response plus partial response plus stable disease ≥ 4 or ≥ 6 months) in the CNS, and safety. RESULTS Thirty-nine patients were treated for a median (range) of 4.5 (0.3-37.3) months at clinical cutoff. Thirty-seven patients discontinued treatment, most commonly because of CNS progression (n = 27); two remained on treatment. CNS ORR was 11% (95% CI, 3 to 25), with four partial responses (median duration of response, 4.6 months). Clinical benefit rate at 4 months and 6 months was 68% and 51%, respectively. Two patients permanently discontinued study treatment because of adverse events (left ventricular dysfunction [treatment-related] and seizure, both grade 3). No grade 5 adverse events were reported. No new safety signals emerged with either agent. CONCLUSION Although the CNS ORR was modest, 68% of patients experienced clinical benefit, and two patients had ongoing stable intracranial and extracranial disease for > 2 years. High-dose trastuzumab for HER2-positive CNS metastases may warrant further study.

Objective/Background We performed a retrospective analysis of longitudinal real-world data (RWD) from patients with breast cancer to replicate results from clinical studies and demonstrate the feasibility of generating real-world evidence. We also assessed the value of transcriptome profiling as a complementary tool for determining molecular subtypes. Methods De-identified, longitudinal data were analyzed after abstraction from records of patients with breast cancer in the United States (US) structured and stored in the Tempus database. Demographics, clinical characteristics, molecular subtype, treatment history, and survival outcomes were assessed according to strict qualitative criteria. RNA sequencing and clinical data were used to predict molecular subtypes and signaling pathway enrichment. Results The clinical abstraction cohort (n = 4000) mirrored the demographics and clinical characteristics of patients with breast cancer in the US, indicating feasibility for RWE generation. Among patients who were human epidermal growth factor receptor 2-positive (HER2+), 74.2% received anti-HER2 therapy, with ∼70% starting within 3 months of a positive test result. Most non-treated patients were early stage. In this RWD set, 31.7% of patients with HER2+ immunohistochemistry (IHC) had discordant fluorescence in situ hybridization results recorded. Among patients with multiple HER2 IHC results at diagnosis, 18.6% exhibited intra-test discordance. Through development of a whole-transcriptome model to predict IHC receptor status in the molecular sequenced cohort (n = 400), molecular subtypes were resolved for all patients (n = 36) with equivocal HER2 statuses from abstracted test results. Receptor-related signaling pathways were differentially enriched between clinical molecular subtypes. Conclusions RWD in the Tempus database mirrors the overall population of patients with breast cancer in the US. These results suggest that real-time, RWD analyses are feasible in a large, highly heterogeneous database. Furthermore, molecular data may aid deficiencies and discrepancies observed from breast cancer RWD.

MEDI4276 is a biparatopic tetravalent antibody targeting two nonoverlapping epitopes in subdomains 2 and 4 of the HER2 ecto-domain, with site-specific conjugation to a tubulysin-based microtubule inhibitor payload. MEDI4276 demonstrates enhanced cellular internalization and cytolysis of HER2-positive tumor cells in vitro. This was a first-in-human, dose-escalation clinical trial in patients with HER2-positive advanced or metastatic breast cancer or gastric cancer. MEDI4276 doses escalated from 0.05 to 0.9 mg/kg (60- to 90-minute intravenous infusion every 3 weeks). Primary endpoints were safety and tolerability; secondary endpoints included antitumor activity (objective response, progression-free survival, and overall survival), pharmacokinetics, and immunogenicity. Forty-seven patients (median age 59 years; median of seven prior treatment regimens) were treated. The maximum tolerated dose was exceeded at 0.9 mg/kg with two patients experiencing dose-limiting toxicities (DLTs) of grade 3 liver function test (LFT) increases, one of whom also had grade 3 diarrhea, which resolved. Two additional patients reported DLTs of grade 3 LFT increases at lower doses (0.4 and 0.6 mg/kg). The most common (all grade) drug-related adverse events (AEs) were nausea (59.6%), fatigue (44.7%), aspartate aminotransferase (AST) increased (42.6%), and vomiting (38.3%). The most common grade 3/4 drug-related AE was AST increased (21.3%). Five patients had drug-related AEs leading to treatment discontinuation. In the as-treated population, there was one complete response (0.5 mg/kg; breast cancer), and two partial responses (0.6 and 0.75 mg/kg; breast cancer)—all had prior trastuzumab, pertuzumab, and ado-trastuzumab emtansine (T-DM1). MEDI4276 has demonstrable clinical activity but displays intolerable toxicity at doses >0.3 mg/kg.

Background: Margetuximab (M) is an investigational Fc-engineered, anti-HER2 monoclonal antibody with the same epitope specificity as trastuzumab (T). Relative to T, Fc engineering of M increases binding affinity for the activating Fc receptor (FcR) CD16A and decreases affinity for the inhibitory FcR CD32B. The SOPHIA trial (NCT02492711) randomized pretreated HER2+ MBC patients to either M or T, each with chemotherapy (C). M+C improved progression-free survival (PFS) benefit over T+C. Infusion related reactions (IRR) have been observed after infusion of therapeutic proteins, typically during the first infusion, with a first-dose incidence of up to 40% for T (Herceptin Prescribing Information®). A retrospective analysis of 197 patients showed 16% IRRs on T, mostly after the first infusion; this rate was lower with (10%) compared to without (19%) premedication (Thompson, 2014). Here, we report IRR safety and tolerability data in the SOPHIA trial patients following HER2-targeted antibody therapy. Methods: The open-label Phase 3 SOPHIA trial enrolled patients with HER2+ MBC after at least 2 prior anti-HER2 therapies, including pertuzumab; 91% in both groups also received ado-trastuzumab emtansine. Randomization of 536 patients was 1:1 to M (15 mg/kg IV q3w) or T (6 [8 loading dose] mg/kg IV q3w), each with Investigator selected C (standard dose capecitabine, eribulin, gemcitabine, or vinorelbine). M was given as 120-minute infusions. T was given as a 90-minute infusion in Cycle 1, then a 30-minute infusion from Cycle 2 onward. Recommended elective premedication included acetaminophen, ibuprofen, diphenhydramine, ranitidine, dexamethasone, or equivalents. IRR safety analyses were conducted on 530 patients (264 M+C and 266 T+C) that received any study therapy. Results: A higher proportion of patients experienced IRRs on the M arm (35 [13.3%]) than on the T arm (9 [3.4%]). Most IRRs in both groups were severity Grade 1 or 2, occurred on Cycle 1 Day 1, and resolved within 24 hours. In patients receiving M, Grade 3 IRR occurred in 4 patients (1.5%), including 3 after vinorelbine and 1 after eribulin. Adverse events associated with Grade 3 IRRs included chills, fever, nausea, diarrhea, dyspnea, and/or hypertension. Two patients receiving M (0.8%) discontinued due to IRR, versus none on T. Of patients with IRRs, the most common symptoms in both treatment groups were chills (M: 17 [48.6%]; T: 5 [55.6%]) and fever (M: 13 [37.1%]; T: 2 [22.2%]). There was no observed hypotension in either group. In both groups, more than half of IRR events were addressed by dose interruption only. All IRRs all were medically manageable. IRR rates were higher in patients without premedication for both groups. Of 264 subjects receiving M, 218 (82.6%) received premedication and 46 (17.4%) did not; IRRs were observed in 28 (12.8%) of those receiving premedication and 7 (15.2%) of those not premedicated. All 4 patients on M with Grade 3 IRRs received premedication, 3 with steroids. Of 266 subjects receiving T, 173 (65%) received premedication and 93 (35%) did not; IRRs were observed in 5 (2.9%) of those receiving premedication and 4 (4.3%) of those not premedicated. IRR risk was unaffected by chemotherapy subgroup or CD16A genotype. Conclusions: In the SOPHIA trial, IRR events occurred in a greater proportion of patients on M than on T. Most were mild to moderate in severity, limited to Cycle 1, and resolved on the same day. Symptom patterns were similar between groups, and premedication did not eliminate the hazard of IRRs in either group. Severe IRRs and discontinuations due to IRRs were rare. IRRs on first infusion of M appear to resemble those observed following first infusion of T. Citation Format: Javier Cortes, Fatima Cardoso, Giuseppe Curigliano, William J Gradishar, Seock-Ah Im, Hope S Rugo, Shakeela W Bahadur, Alfredo Falcone, Serafin Morales Murillo, David A Riseberg, Antonino Musolino, Trevor M Feinstein, Miguel H Abreu, Young-Hyuck Im, Yelena Novik, Timothy Pluard, Lupe G Salazar, Rossana Berardi, Viorela Pop, Shengyan Hong, Kenneth Jacobs, Edwin Rock, Mark D Pegram. Infusion related reactions in the phase 3 SOPHIA trial of margetuximab + chemotherapy vs trastuzumab + chemotherapy in patients with pretreated HER2+ metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-24.

Depletion of mitochondrial copper, which shifts metabolism from respiration to glycolysis and reduces energy production, is known to be effective against cancer types that depend on oxidative phosphorylation. However, existing copper chelators are too toxic or ineffective for cancer treatment. Here we develop a safe, mitochondria-targeted, copper-depleting nanoparticle (CDN) and test it against triple-negative breast cancer (TNBC). We show that CDNs decrease oxygen consumption and oxidative phosphorylation, cause a metabolic switch to glycolysis and reduce ATP production in TNBC cells. This energy deficiency, together with compromised mitochondrial membrane potential and elevated oxidative stress, results in apoptosis. CDNs should be less toxic than existing copper chelators because they favorably deprive copper in the mitochondria in cancer cells instead of systemic depletion. Indeed, we demonstrate low toxicity of CDNs in healthy mice. In three mouse models of TNBC, CDN administration inhibits tumor growth and substantially improves survival. The efficacy and safety of CDNs suggest the potential clinical relevance of this approach.

Trastuzumab and the related antibody-drug conjugate (ADC), ado-trastuzumab emtansine (T-DM1), both target HER2-overexpressing cells. Together, these drugs have treatment indications in both early-stage and metastatic settings for HER2+ breast cancer. T-DM1 retains the antibody functionalities of trastuzumab and adds the potency of a cytotoxic maytansine payload. Interestingly, in the clinic, T-DM1 cannot always replace the use of trastuzumab plus chemotherapy administered together as single agents. We hypothesize that this failure may be due in part to the limited systemic exposure achieved by T-DM1 relative to trastuzumab because of toxicity-related dosing constraints on the ADC. We have developed a trastuzumab-based ADC site-specifically conjugated to maytansine through a noncleavable linker. This construct, termed CAT-01-106, has a drug-to-antibody ratio (DAR) of 1.8, approximately half the average DAR of T-DM1, which comprises a mixture of antibodies variously conjugated with DARs ranging from 0-8. The high DAR species present in T-DM1 contribute to its toxicity and limit its clinical dose. CAT-01-106 showed superior in vivo efficacy compared to T-DM1 at equal payload dosing and was equally or better tolerated compared to T-DM1 at equal payload dosing up to 120 mg/kg in Sprague-Dawley rats and 60 mg/kg in cynomolgus monkeys. CAT-01-106 also showed improved pharmacokinetics in rats relative to T-DM1, with 40% higher ADC exposure levels. Together, the data suggest that CAT-01-106 may be sufficiently tolerable to enable clinical dosing at trastuzumab-equivalent exposure levels, combining the functions of both the antibody and the payload in one drug and potentially improving patient outcomes.

Expression of human epidermal growth factor receptor 2 (HER2) in breast cancer defines a subset of patients (∼15%-20%) who are candidates for anti-HER2 therapies, most notably, trastuzumab, pertuzumab, antibody drug conjugates (eg, T-DM1), and tyrosine kinase inhibitor (TKI) drugs (eg, lapatinib and neratinib), all of which have dramatically changed the prognosis for this aggressive subtype of breast cancer. A roundtable meeting of the Breast Cancer Therapy Expert Group (BCTEG) was convened in March 2018 in an effort to discuss and clarify, from the perspective of the practicing community oncologist, recent developments in the diagnosis and treatment of HER2-positive (HER2+) breast cancer. Members of the group selected 4 key topics for discussion prior to the meeting, including diagnosis of HER2+ disease, and its treatment in the neoadjuvant, adjuvant, and metastatic settings. Approved testing methods, such as immunohistochemistry and fluorescence in situ hybridization, are used to demonstrate overexpression and/or amplification of HER2 in breast tumors, and established clinical guidelines are used to appropriately define treatment plans for patients with HER2+ disease. The panel acknowledges a range of treatment options now available for treatment of HER2+ breast cancer in the neoadjuvant, adjuvant, and advanced/metastatic settings, although it is noted that many controversies remain, including the optimal sequence of therapies, the most appropriate treatment(s) for subsets of patients with HER2+ disease (eg, hormone receptor-negative or -positive/HER2+), and uncertainties surrounding the diagnosis and definition of HER2+ disease. The current report summarizes the discussion of the BCTEG panel on this topic.

Background: Chemotherapy treatments with robust efficacy that preserve quality of life are needed. Tesetaxel is a novel, oral taxane that has potential advantages over currently available taxanes, including: oral administration with a low pill burden and once every 3 week (Q3W) dosing; no observed hypersensitivity reactions; preclinical evidence of central nervous system (CNS) penetration; and improved activity against chemotherapy-resistant tumors. More than 600 patients have been treated with tesetaxel in clinical studies. Tesetaxel had robust monotherapy activity in a Phase 2 study in 38 patients with HER2-, HR+ MBC, with a confirmed objective response rate (ORR) per RECIST 1.1 of 45% and median PFS of 5.4 months. The confirmed ORR in taxane-pretreated patients also was 45%. Preclinical and clinical studies suggest that reducing the dose of capecitabine in combination with a taxane may result in reduced toxicity without a reduction in efficacy. CONTESSA investigates tesetaxel plus a reduced dose of capecitabine as an all-oral regimen in patients with HER2-, HR+ MBC. Trial design: CONTESSA is a 600-patient, multinational, multicenter, randomized (1:1), Phase 3 registration study comparing tesetaxel (27 mg/m2 on Day 1 of a 21-day cycle) plus a reduced dose of capecitabine (1,650 mg/m2/day on Days 1-14 of a 21-day cycle) to the approved dose of capecitabine alone (2,500 mg/m2/day on Days 1-14 of a 21-day cycle) in patients with HER2-, HR+ MBC who have received no more than one chemotherapy regimen for advanced disease and have received a taxane in the (neo)adjuvant setting. Patients with known CNS metastases are eligible. The primary endpoint is progression-free survival (PFS) assessed by an Independent Radiologic Review Committee (IRC). CONTESSA is 90% powered to detect a 42% improvement in PFS (HR = 0.71). Secondary endpoints are overall survival, ORR and disease control rate. Enrollment began in December 2017. In June 2019, the Independent Data Monitoring Committee for CONTESSA recommended that the study continue with no modifications following a planned interim efficacy futility analysis. The interim efficacy futility analysis was based on a pre-specified analysis of the first approximate 100 PFS events that occurred in the study. For further information on this trial, email joconnell@odonate.com or visit clinicaltrials.gov (NCT03326674). Citation Format: Joyce O'Shaughnessy, Martine Piccart, Lee Schwartzberg, Javier Cortes, Nadia Harbeck, Seock-Ah Im, Hope Rugo, Michael Untch, Denise Yardley, Igor Bondarenko, Veronique Dieras, Mark Pegram, Stew Kroll, Joseph O'Connell, Jeff Vacirca, Thomas Wei, Kevin Tang, Andrew Seidman. CONTESSA: A multinational, multicenter, randomized, phase 3 registration study of tesetaxel plus a reduced dose of capecitabine in patients with HER2-, hormone receptor + (HR+) metastatic breast cancer (MBC) who have previously received a taxane [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT1-08-09.

Background: There is an unmet need for evidence-based systemic therapies for pts with HER2-positive MBC and progressive brain metastases. Despite assumptions that monoclonal antibodies do not cross the blood-brain barrier, molecular imaging in pts shows localization of 89Zr-trastuzumab to brain metastases. Furthermore, preclinical data support dose-dependent activity of H in intracranial tumor models. The PATRICIA study (NCT02536339) evaluated safety and efficacy of P plus high-dose H in pts with HER2-positive MBC with CNS metastases and CNS progression after RT. Herein, we present results from the primary efficacy analysis of PATRICIA. Methods: PATRICIA was a US-based, phase II, open-label, single arm study. Eligible pts had measurable (≥10 mm) CNS disease that had progressed after CNS-directed RT, in the setting of stable extracranial disease. CNS-directed RT included whole-brain RT (WBRT) or stereotactic radiosurgery (SRS) and must have been completed ≥60 days before study entry. Pts received P (840 mg loading dose, then 420 mg every 3 weeks) and high-dose H (6 mg/kg weekly), which continued until progression (CNS or systemic) or unacceptable toxicity. Pts could continue their existing systemic anti-cancer therapy during the study, with the exception of trastuzumab emtansine (T-DM1) or lapatinib. Switch of other anti-cancer therapy was not permitted during the study. Restaging evaluations including brain MRI were completed every 2 cycles. The primary efficacy endpoint was confirmed objective response rate (ORR) in the CNS per Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM) criteria. Secondary endpoints included duration of response (DOR), clinical benefit rate (CBR) in the CNS, and safety. Samples were collected for exploratory pharmacokinetic analyses on Day 1 of weeks 1, 4, 10, and 16. Results: From 15 Dec 2015 to 18 May 2017, 40 pts were enrolled across 16 sites. Median age was 48 (range 34–69) years, with 33% and 67% of pts having an Eastern Cooperative Oncology Group Performance Status score of 0 or 1, respectively. 41% of pts had received prior WBRT only, 28% had received prior SRS only, and 31% had received both. At the data cut off (1 May 2019), of 39 treated pts, 2 remained on study treatment and 37 discontinued treatment, most commonly due to CNS progression (n=27). Median treatment duration was 4.5 (range 0.3–37.3) months. Four pts in the efficacy population (N=37) experienced a confirmed partial response (Table), leading to an ORR of 11% (95% confidence interval [CI], 3–25%). Response durations were 3.2, 3.3, 4.6, and 5.6 months (median DOR 4.6 months). The CBR (complete response + partial response + stable disease [SD] of ≥4 or ≥6 months) was 68% (SD ≥4 months) and 51% (SD ≥6 months). Results from exploratory pharmacokinetic analyses confirmed greater H exposure with the high-dose schedule. The adverse event profile was similar to that previously reported for P and H, with no new safety signals. One pt discontinued treatment due to an adverse event (grade 3 left ventricular dysfunction, considered related to study treatment). No Grade 5 adverse events were reported. Conclusions: The CNS ORR of 11%, ≥6-month CBR of 51%, and lack of any new safety signals suggest that P plus high-dose H may have clinical utility in some pts with HER2-positive MBC with progressive CNS metastases. Table. Efficacy within the CNS per RANO-BM criteriaEfficacy population (N=37)n (%)95% CIORR*4 (11)3, 25CBR (CR + PR + stable disease [SD] ≥4 months)25 (68)50, 82CBR (CR + PR + SD ≥6 months)19 (51)34, 68Confirmed best response (SD ≥4 months)CR0—PR4 (11)—SD ≥4 months21 (57)—Pts without clinical benefit12 (32)—Confirmed best response (SD ≥6 months)CR0—PR4 (11)—SD ≥6 months15 (41)—Pts without clinical benefit18 (49)—*Confirmed complete response (CR) or confirmed partial response (PR). Citation Format: Nancy U Lin, Priya Kumthekar, Solmaz Sahebjam, Nuhad Ibrahim, Anita Fung, Anna Cheng, Alan Nicholas, Bei Wang, Mark Pegram. Pertuzumab (P) plus high-dose trastuzumab (H) for the treatment of central nervous system (CNS) progression after radiotherapy (RT) in patients (pts) with HER2-positive metastatic breast cancer (MBC): Primary efficacy analysis results from the phase II PATRICIA study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-18-03.

Background: Margetuximab (M) is an investigational Fc-engineered anti-HER2 monoclonal antibody that targets the same epitope as trastuzumab (T) and exerts similar antiproliferative effects. Compared with T, M has higher affinity for both the 158V (high-binding) and 158F (low-binding) allotypes of the activating Fc receptor CD16A. M enhances innate immunity, including CD16A-mediated antibody-dependent cellular cytotoxicity, and does so more effectively than T in vitro. Based on ex vivo experiments with cells collected from patients (pts) before and after treatment, M induces adaptive immunity, including enhanced T-cell clonality and induction of HER2-specific T- and B-cell responses. The SOPHIA trial (NCT02492711) showed that in pts with pretreated HER2+ metastatic breast cancer (MBC), M+chemotherapy improved progression-free survival vs T+chemotherapy, with comparable safety. M is intended to be dosed at 15 mg/kg every 3 weeks, with infusions over 120 min at every cycle (C). A substudy of SOPHIA was conducted to evaluate the safety and tolerability of reduced infusion times from C2 onward. Methods: Eligible pts had HER2+ MBC after ≥4 lines of prior therapy for MBC, including prior T, pertuzumab, and ado-T emtansine. Enrolled pts received a 120-min M infusion, with or without chemotherapy, in C1, then either 60- or 30-min infusions in C2 and beyond. This single-arm substudy was unblinded, with no comparator. The primary objective was incidence of Grade 3 or greater infusion-related reactions (IRRs) by the end of C2. Incidence of all IRRs was a secondary objective. Results: Of 88 pts enrolled, 69 received M+chemotherapy and 19 received M alone. Mean age was 54.5 years; 99% were female and 71% white. The median number of cycles of M received was 3 (range 1-17). Overall, 7 pts were assigned to received 60-min M infusions starting at C2 (range 1-17 cycles), and 76 pts were assigned to received 30-min M infusions starting at C2 (range 1-14 cycles). Five pts did not receive C2 treatment due to non-radiologic progressive disease, unrelated adverse event (AE), patient or physician decision, or loss to follow-up. Eighty (91%) pts had premedication for IRRs. No pt had Grade ≥3 IRR. Overall, 18 (21%) had IRRs (2 Grade 1, 16 Grade 2), all but 1 of which occurred in C1 (120 min). Of the 18 pts with IRRs, 17 (94%) were premedicated and 10 (56%) were treated for IRRs. The overall rate of IRRs in premedicated pts was 21% (17/80) and in non-premedicated pts was 13% (1/8). One pt experienced IRRs in both C1 and C2 (Grade 2 in C1 and Grade 1 in C2); the same patient then received 6 additional cycles of M (30 min) with no IRRs after C2 (C3-8) and had no premedication after C1. No pt discontinued treatment due to an IRR. Of 88 pts enrolled, 85 (97%) pts experienced an AE, and 7 (8%) had Grade ≥3 AEs. Fifty (57%) pts had M-related AEs. The most common (>5% of pts) M-related AEs were IRRs in 17 (19%), fatigue in 9 (10%), diarrhea in 5 (6%), and aspartate aminotransferase increase in 5 (6%). Serious AEs occurred in 13/88 pts (15%), none of which were considered M-related by the investigator. Conclusions: In this heavily pretreated population, shorter M infusion times did not lead to an increase in IRRs. IRRs were most likely to occur during C1 when the infusion time was 120 min. No Grade ≥3 IRRs were observed. Of 18 pts with Grade 1-2 IRRs, only 1 had an IRR after C1. These results showed that the acceptable safety and tolerability profile of M was maintained even after infusion time is reduced to 30-min from C2 onward. Shorter infusion times may reduce the burden of chronic M therapy on pts, caregivers, and clinic staff. Citation Format: William J. Gradishar, Seock-Ah Im, Fatima Cardoso, Javier Cortes, Giuseppe Curigliano, Mark D. Pegram, Antonino Musolino, Rosanna Berardi, Michelino De Laurentiis, Shakeela W. Bahadur, Young-Hyuck Im, Cynthia Lynch, Yelena Novik, Sutton Edlich, Edwin Rock, Shengyan Hong, Hope S. Rugo, SOPHIA Study Group. Phase 3 SOPHIA study of margetuximab + chemotherapy vs trastuzumab + chemotherapy in patients with HER2+ metastatic breast cancer after prior anti-HER2 therapies: Infusion time substudy results [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-18-04.

Efficacy data from the KATHERINE clinical trial, comparing the HER2-directed antibody-drug conjugate (ADC) ado-trastuzumab emtansine (T-DM1) to trastuzumab in patients with early-stage HER2-amplified/overexpressing breast cancer with residual disease after neoadjuvant therapy, demonstrates superiority of T-DM1 (HR for invasive disease or death, 0.50; P < 0.001). This establishes foundational precedent for ADCs as effective therapy for treatment of subclinical micrometastasis in an adjuvant (or post-neoadjuvant) early-stage solid tumor setting. Despite this achievement, general principles from proposed systems pharmacokinetic modeling for intracellular processing of ADCs indicate potential shortcomings of T-DM1: (i) Cmax limited by toxicities; (ii) slow internalization rate; (iii) resistance mechanisms due to defects in intracellular trafficking [loss of lysosomal transporter solute carrier family 46 member 3, (SLC46A3)], and increased expression of drug transporters MDR1 and MRP1; and (iv) lack of payload bystander effects limiting utility in tumors with heterogeneous HER2 expression. These handicaps may explain the inferiority of T-DM1–based therapy in the neoadjuvant and first-line metastatic HER2+ breast cancer settings, and lack of superiority to chemotherapy in HER2+ advanced gastric cancer. In this review, we discuss how each of these limitations is being addressed by manipulating internalization and trafficking using HER2:HER2 bispecific or biparatopic antibody backbones, using site-specific, fixed DAR conjugation chemistry, and payload swapping to exploit alternative intracellular targets and to promote bystander effects. Newer HER2-directed ADCs have impressive clinical activity even against tumors with lower levels of HER2 receptor expression. Finally, we highlight ongoing clinical efforts to combine HER2 ADCs with other treatment modalities, including chemotherapy, molecularly targeted therapies, and immunotherapy.

Background Margetuximab (M) is an investigational Fc-engineered anti-HER2 monoclonal antibody that targets the same epitope as trastuzumab (T). Compared with T, M has higher affinity for both the 158V (high-binding) and 158F (low-binding) allotypes of the activating Fc receptor CD16A. M enhances innate immunity more effectively than T in vitro, including CD16A-mediated antibody-dependent cellular cytotoxicity. Samples collected from patients (pts) before and after single-agent treatment also demonstrate that M induces HER2-specific adaptive immune responses, including both T- and B-cell responses. The SOPHIA trial (NCT02492711) in pts with pretreated HER2+ MBC showed that M+chemotherapy (chemo) improved progression-free survival vs T+chemo, with comparable safety. A pooled analysis of M safety across 3 clinical trials is presented. Methods Study 01 (NCT01148849), an ongoing Phase 1 dose-finding/safety study of M monotherapy, enrolled 66 pts with advanced HER2+ carcinomas, including 27 with MBC. Study 02 (NCT01828021), a completed Phase 2 study of M monotherapy in low-expressing HER2+ MBC, enrolled 25 pts. Study 04 (NCT02492711), an ongoing Phase 3 study in pts with pretreated HER2+ MBC to compare M + chemo vs T + chemo, randomized 536 pts, of whom 264 and 265 received M and T, respectively. The pooled safety population includes all pts who received any M in Study 01 (cutoff 01Oct2015), Study 02 (cutoff 02Aug2017), and Study 04 (cutoff 10OCT2018). Treatment-emergent adverse events (AEs), defined as AEs that began or worsened in severity on or after first dose of study drug through an End of Treatment Visit or 28 days after last study treatment, are reported. Results Of 355 pts that received at least 1 dose of M, 295 received 15 mg/kg Q3W, and 60 received other doses from 0.1 - 18 mg/kg. Median (mean, range) number of cycles for all dose levels was 5.0 (6.6, 1-43), higher on Study 04 (6.0) than Study 01 (1-3 across dose groups) or Study 02 (2.0). Most pts (347 [97.7%]) experienced at least 1 AE, and about half (173 [48.7%]) had at least 1 Grade >/= 3 AE. Serious AE (SAE) incidence across studies was low (58 [16.3%]), and 21 pts (5.9%) discontinued M due to AEs. Most frequently reported AEs (>/= 20%) were fatigue (124 [34.9]), nausea (103 [29.0%]), diarrhea (75 [21.1%]), and neutropenia (75 [21.1%]). Blood/lymphatic system disorders were the most frequent events by SOC, and largely restricted to Study 04. Increased neutropenia on M (26.1%), relative to T (20.4%), was observed in Study 04 yet both febrile neutropenia (M 3.0%, T 4.5%) and infections (M 36.4%, T 39.6%) were higher on T. By contrast, Study 01 and Study 02 revealed no tendency of M monotherapy to cause neutropenia. Overall, infusion related reactions (IRRs) were observed in 51 pts (14.4%), primarly at first infusion, including serious IRRs in 5 (1.4%). Also, 34 pts (9.6%) had > 15% reduction in LVEF with a median time to > 15% reduction of 49 days. In all pts with complete follow-up, these LVEF reductions were asymptomatic and reversible. No M-induced cardiac conduction abnormalities were noted. In Study 04, similar proportions in both groups experienced AEs (M 97.7%, T 96.2%), including Grade >/= 3 AEs (M 52.3%, T 48.3%), SAEs (M 14.8%, T 17.4%), discontinuations due to AEs (M 3.0%, T 2.6%), and deaths due to AEs (M 0.8%, T 0.8%). As of the 23Feb2020 safety update, 2 pts remain on M in Study 01, after 116 and 109 cycles (6.7 and 6.3 years), respectively. In Study 04, 16 pts (6%) continued on M, and 7 (2.6%) remained on T. Discussion M has demonstrated an acceptable safety profile across Phase 1, 2, and 3 studies. It has been administered for over 6 years without long-term cumulative safety issues. Combined M plus chemotherapy Q3W demonstrated acceptable safety and tolerability, similar to that for T plus chemotherapy Q3W in Study 04. Citation Format: Seock-Ah Im, Fatima Cardoso, Javier Cortes, Giuseppe Curigliano, Mark D. Pegram, Hope S. Rugo, Ursa Brown-Glaberman, Denise A. Yardley, Sung-Bae Kim, Maaike de Boer, Zbigniew Nowecki, Vesna Glavicic, Ido Wolf, Nele Claes, Joo Hyuk Sohn, Thomas Bachelot, Peter A. Kaufman, Jan Baughman, Shengyan Hong, Kenneth Jacobs, Edwin Rock, William J. Gradishar. Integrated safety summary of single agent and combination margetuximab in phase 1, 2, and 3 studies of HER2-positive advanced cancers and metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-12.

Background: Rintodestrant (G1T48) is a potent oral selective estrogen receptor degrader (SERD) that competitively binds to the estrogen receptor (ER) and blocks ER signaling in tumors resistant to other endocrine therapies. Preliminary results from Part 1 dose escalation showed robust target engagement on 18F-fluoroestradiol positron emission tomography (FES-PET), a favorable safety profile, and encouraging antitumor activity in patients with heavily pretreated ER+/HER2- advanced breast cancer (ABC), including those with ESR1 mutations (Dees et al., ESMO 2019 [abstract #3587]). Here, we present updated results from dose escalation and expansion (Parts 1 and 2). Methods: This Phase 1, first-in-human, open-label study evaluated rintodestrant monotherapy in women with ER+/HER2- ABC after progression on endocrine therapy. Part 1 was a 3+3 dose escalation (200-1000 mg once daily [QD]); Part 2 expanded 600 and 1000 mg QD; and Part 3 was added to assess rintodestrant with palbociclib in patients in earlier lines in the advanced setting. Primary objectives included dose-limiting toxicities (DLTs), maximum tolerated dose (MTD), safety, and recommended Phase 2 dose. Secondary objectives included pharmacokinetics and antitumor activity (RECIST v1.1). Exploratory objectives included pharmacodynamic inhibition of ER target engagement (FES-PET), mutation profiling (cell-free DNA [cfDNA]), and change in ER expression from baseline to on-treatment tumor biopsies. Results: As of May 13, 2020, 67 patients (Part 1: n = 26; Part 2: n = 41) were treated, with a median age of 61 years (range 34-83) and ECOG PS of 0 (49%) or 1 (51%). Median number of prior lines in the advanced setting was 2 (range 0-9), including prior fulvestrant (64%), CDK4/6 inhibitor (69%), mTOR inhibitor (22%), and/or chemotherapy (46%). Median number of prior lines of endocrine therapy in the advanced setting was 2 (range 0-5), with 61% of patients having received ≥2 lines. Treatment-related adverse events (TRAEs) were reported in 70% of patients. The most common TRAEs in ≥10% of patients included hot flush (24%), fatigue (21%), nausea (19%), diarrhea (18%), and vomiting (10%), mostly grade 1 or 2. No DLTs were reported and MTD was not reached. Dose reduction due to TRAEs occurred in 1 patient (1%), with elevated transaminases (grade 3 ALT and grade 2 AST) at 600 mg. Serious TRAEs occurred in 2 patients at 1000 mg (grade 5 cerebral hemorrhage in the setting of low molecular weight heparin and grade 2 upper abdominal pain). Two patients (3%) discontinued treatment due to TRAEs. Overall, the frequency of patients with TRAEs at 800 mg was comparable with that at 600 mg (57% vs 63%) and less than that at 1000 mg (81%). Of 67 patients, 16 were on study treatment for ≥24 weeks and 3 (n = 1 at 600 mg; n = 2 at 1000 mg, including 1 with ESR1 mutation) had a confirmed partial response (clinical benefit rate [CBR]: 28%). FES-PET standard uptake values decreased at week 4 with a mean reduction of 87% (±8%) at doses ≥ 600 mg. Of 59 patients tested for baseline cfDNA, 41% harbored ≥1 ESR1 mutation, with a similar CBR in both groups (33% in ESR1 mutant and 29% in ESR1 wild-type). Seven of 9 patients had a decrease in ER immunohistochemistry H-score at both 600 and 1000 mg (median [range]: -27.8% [-33.8%, -3.4%]), irrespective of ESR1 mutation status. Based on safety, efficacy, and ER degradation, 800 mg was selected as the optimal dose for further study. Conclusions: Rintodestrant continues to demonstrate an excellent safety/tolerability profile across all doses, with promising antitumor activity in patients with heavily pretreated ER+/HER2- ABC, including those with tumors harboring ESR1 mutations. Part 3 of this study, evaluating rintodestrant 800 mg QD with palbociclib in a more endocrine-sensitive population, is ongoing (NCT03455270). Citation Format: Philippe Aftimos, Patrick Neven, Mark Pegram, Catharina Willemien Menke-van der Houven van Oordt, E. Claire Dees, Carolien Schröder, Agnes Jager, Iurie Bulat, Linnea Chap, Marina Maglakelidze, Erika Hamilton, Massimo Cristofanilli, Susanna Ulahannan, Jorianne Boers, Ramsha Iqbal, Adrian Crijanovschi, Curt D Wolfgang, Wenli Tao, Christina Sipes, Rajesh Malik, Sarika Jain. Rintodestrant (G1T48), an oral selective estrogen receptor degrader in ER+/HER2- locally advanced or metastatic breast cancer: Updated phase 1 results and dose selection [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS12-04.

Significance This study demonstrates the efficacy of combining macrophage-checkpoint inhibition with tumor-specific antibodies for cancer immunotherapy. The combination of anti-CD47 (magrolimab) and anti-HER2 (trastuzumab) antibodies eliminated HER2+ breast cancer cells with increased efficacy due to the enhancement of antibody-dependent cellular phagocytosis by macrophages, even when the cancer cells were tolerant to trastuzumab-induced antibody-dependent cellular cytotoxicity by natural killer cells. We believe these findings present a promising therapeutic approach for treating HER2+ breast cancer patients whose tumors are either sensitive or resistant to trastuzumab treatment, as long as the cells harbor the HER2 trastuzumab-binding epitope. This study supports the notion that combining CD47 blockade with existing macrophage FcR-engaging tumor-specific antibodies may be an effective approach for treating a wide range of cancers., Trastuzumab, a targeted anti-human epidermal-growth-factor receptor-2 (HER2) monoclonal antibody, represents a mainstay in the treatment of HER2-positive (HER2+) breast cancer. Although trastuzumab treatment is highly efficacious for early-stage HER2+ breast cancer, the majority of advanced-stage HER2+ breast cancer patients who initially respond to trastuzumab acquire resistance to treatment and relapse, despite persistence of HER2 gene amplification/overexpression. Here, we sought to leverage HER2 overexpression to engage antibody-dependent cellular phagocytosis (ADCP) through a combination of trastuzumab and anti-CD47 macrophage checkpoint immunotherapy. We have previously shown that blockade of CD47, a surface protein expressed by many malignancies (including HER2+ breast cancer), is an effective anticancer therapy. CD47 functions as a “don’t eat me” signal through its interaction with signal regulatory protein-α (SIRPα) on macrophages to inhibit phagocytosis. Hu5F9-G4 (magrolimab), a humanized monoclonal antibody against CD47, blocks CD47’s “don’t eat me” signal, thereby facilitating macrophage-mediated phagocytosis. Preclinical studies have shown that combining Hu5F9-G4 with tumor-targeting antibodies, such as rituximab, further enhances Hu5F9-G4’s anticancer effects via ADCP. Clinical trials have additionally demonstrated that Hu5F9-G4, in combination with rituximab, produced objective responses in patients whose diffuse large B cell lymphomas had developed resistance to rituximab and chemotherapy. These studies led us to hypothesize that combining Hu5F9-G4 with trastuzumab would produce an anticancer effect in antibody-dependent cellular cytotoxicity (ADCC)-tolerant HER2+ breast cancer. This combination significantly suppressed the growth of ADCC-tolerant HER2+ breast cancers via Fc-dependent ADCP. Our study demonstrates that combining trastuzumab and Hu5F9-G4 represents a potential new treatment option for HER2+ breast cancer patients, even for patients whose tumors have progressed after trastuzumab.

Introduction: Although many current cancer therapies are effective, the mortality rate globally is unacceptably high. Cancer remains the second leading cause of death worldwide after heart disease and has caused nearly 10 million deaths in 2018. Additionally, current preventive therapies for cancer are underdeveloped, undermining the quality of life of high-risk individuals. Therefore, new treatment options for targeting cancer are urgently needed. In a recent study, researchers adopted an autologous iPSC-based vaccine to present a broad spectrum of tumor antigens to the immune system and succeeded in orchestrating a strong prophylactic immunity towards multiple types of cancer in mice. Areas covered: In this review, we provide an overview of how cancer develops, the role of immune surveillance in cancer progression, the current status and challenges of cancer immunotherapy as well as the genetic overlap between pluripotent stem cells and cancer cells. Finally, we discuss the rationale for an autologous iPSC-based vaccine and its applications in murine cancer models. Expert opinion: The autologous iPSC-based vaccine is a promising preventive and therapeutic strategy for fighting various types of cancers. Continuing efforts and clinical/translational follow-up studies may bring an autologous iPSC-based cancer vaccination approach from bench to bedside.

e18595 Background: Multidisciplinary tumor boards (TBs) are a key component of high-quality oncology care. Access is variable, particularly outside the academic setting, and limited access likely disproportionately impacts underserved patient populations and may contribute to healthcare disparities. Virtual tumor boards (VTBs) may provide a solution. Methods: Objectives of this endeavor are to test the feasibility of conducting VTBs and assess their perceived benefit and educational value. Expert US faculty formed VTB panels via an online platform to discuss complex cases submitted by clinicians. Each panel included a moderator and a radiologist, as well as a medical, radiation and surgical oncologist. After the panel discussion, written recommendations and video recordings (de-identified) were shared with submitters. Recordings were available online to viewers with embedded questions to assess learning. Submitters were surveyed as to their perceived benefit of the discussion. Viewers were surveyed to assess the educational value. Results: From 07/2020-12/2021, 323 cases (97 breast, 109 thoracic, 49 gastrointestinal, 37 genitourinary, 31 hematologic) were submitted by 48 clinicians to 38 VTBs. Submitters were surveyed with a 73% response rate; 100% reported they were likely to submit a future case for discussion and that they believe the VTB will improve care for patients. Viewers (n = 39) were surveyed with a 72% response rate and included trainees and APPs working in medical, radiation, and surgical oncology as well as radiology. All viewers endorsed that the videos were a good educational resource, and that they would use them in the future. Both embedded questions were answered 74% of the time (315/425); answers post-viewing changed 43% of the time (137/315). Conclusions: VTBs are feasible and lead to a high degree of satisfaction among case submitters. In this cohort, users reported that their patient management changed based on the discussion. Of those who discussed the case at their own TB, most felt that the VTB expanded upon prior recommendations. A large proportion of users stated that their case was not discussed at an internal TB, suggesting the VTB may address an unmet need. Those who watched the videos found them to be a good resource and would use them in the future. Data from larger cohorts will be key in understanding the full impact of this endeavor, particularly in helping to address healthcare disparities.[Table: see text]

INTRODUCTIONWe performed a retrospective analysis of longitudinal real-world data (RWD) from breast cancer patients to replicate results from clinical studies and demonstrate the feasibility of generating real-world evidence. We also assessed the value of transcriptome profiling as a complementary tool for determining molecular subtypes.PATIENTS AND METHODSDe-identified, longitudinal data were analyzed after abstraction from U.S. breast cancer patient records structured and stored in the Tempus database. Demographics, clinical characteristics, molecular subtype, treatment history, and survival outcomes were assessed according to strict qualitative criteria. RNA sequencing and clinical data were used to predict molecular subtypes and signaling pathway enrichment.RESULTSThe clinical abstraction cohort (n=4,000) mirrored U.S. breast cancer demographics and clinical characteristics indicating feasibility for RWE generation. Among HER2+ patients, 74.2% received anti-HER2 therapy, with ~70% starting within 3 months of a positive test result. Most non-treated patients were early stage. In this RWD set, 31.7% of patients with HER2+ IHC had discordant FISH results recorded. Among patients with multiple HER2 IHC results at diagnosis, 18.6% exhibited intra-test discordance. Through development of a whole-transcriptome model to predict IHC receptor status in the molecular sequenced cohort (n=400), molecular subtypes were resolved for all patients (n=36) with equivocal HER2 statuses from abstracted test results. Receptor-related signaling pathways were differentially enriched between clinical molecular subtypes.CONCLUSIONRWD in the Tempus database mirrors the overall U.S. breast cancer population. These results suggest real-time, RWD analyses are feasible in a large, highly heterogeneous database. Furthermore, molecular data may aid deficiencies and discrepancies observed from breast cancer RWD.

Triple-negative breast cancer (TNBC), defined as breast cancer lacking expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2), accounts for up to 20% of all breast cancer, and it occurs at a higher frequency in younger, African American, and Hispanic women. Compared to breast cancers that are hormone receptor and/or HER2 positive, TNBC has an aggressive clinical course and worse prognosis. Because TNBC is by definition unresponsive to endocrine therapy (eg, tamoxifen, aromatase inhibitors) and HER2-directed therapies (eg, trastuzumab), chemotherapy continues to play an important role. TNBC constitutes a molecularly heterogeneous group of tumors that can vary in response to treatment, and clinical management can be challenging, particularly for the practicing community oncologist, for whom breast cancer may be only one of many tumor types encountered. In January 2020, the Breast Cancer Therapy Expert Group (BCTEG) convened a roundtable discussion on the topic of advances in the treatment of TNBC. Topics discussed included histopathologic classification/definition of TNBC, neoadjuvant strategies, adjuvant chemotherapy (with special emphasis on management of patients who do not experience a pathologic complete response), and treatment of metastatic disease. Also reviewed was the wide range of emerging pathways and therapies currently under investigation to expand TNBC treatment options, including immunotherapies and poly(ADP-ribose) polymerase (PARP) inhibitors. This article summarizes the BCTEG discussion and highlights the key opinions relating to the treatment of patients with TNBC.

Adjuvant chemotherapy in breast cancer patients causes immune cell depletion at an age when the regenerative capacity is compromised. Successful regeneration requires the recovery of both quantity and quality of immune cell subsets. Although immune cell numbers rebound within a year after treatment, it is unclear whether overall compositional diversity is recovered. We investigated the regeneration of immune cell complexity by comparing peripheral blood mononuclear cells from breast cancer patients ranging from 1–5 years after chemotherapy with those of age-matched healthy controls using mass cytometry and T cell receptor sequencing. These data reveal universal changes in patients’ CD4(+) T cells that persisted for years and consisted of expansion of Th17-like CD4 memory populations with incomplete recovery of CD4(+) naive T cells. Conversely, CD8(+) T cells fully recovered within a year. Mechanisms of T cell regeneration, however, were unbiased, as CD4(+) and CD8(+) T cell receptor diversity remained high. Likewise, terminal differentiated effector memory cells were not expanded, indicating that regeneration was not driven by recognition of latent viruses. These data suggest that, while CD8(+) T cell immunity is successfully regenerated, the CD4 compartment may be irreversibly affected. Moreover, the bias of CD4 memory toward inflammatory effector cells may impact responses to vaccination and infection.

Background: CTX + dual HER2-targeting monoclonal antibodies (mAb) remains a standard of care for treatment (Tx) of both HER2+ early-stage and MBC. However, when the SOPHIA trial was launched, limited Tx options existed after progression on T, pertuzumab (P), and ado-trastuzumab emtansine. M, an Fc-engineered anti-HER2 mAb, targets the same epitope as T and exerts similar antiproliferative effects. M enhances CD16A-mediated ADCC compared to T. Furthermore, M treatment is associated with increased HER2-specific T- and B-cell responses and increased T-cell clonality compared to baseline. The phase 3 SOPHIA (NCT02492711) study demonstrated PFS benefit of M vs T, both + CTX, in HER2+ MBC pts. M improved PFS over T, with a 24% relative risk reduction (HR .76; 95% CI .59-.98; P=.033; median, 5.8 [95% CI 5.5-7.0] months (mo) vs 4.9 [95% CI 4.2-5.6] mo (Rugo HS, et al. JAMA Oncol 2021), resulting in FDA approval. Median OS after 270 mortality events (2nd interim analysis) was 21.6 mo with M vs 19.8 mo with T (HR .89; 95% CI .69-1.13; P=.33). Here we report final OS after 385 events, as well as updated safety.Methods: Pts with disease progression after ≥2 lines of anti-HER2 Tx, including P, and 1-3 lines of Tx for HER2+ MBC were randomized 1:1 to CTX + either M (15 mg/kg) or T (8 mg/kg loading dose, then 6 mg/kg), both given IV every 3 weeks. Randomization was stratified by number of metastatic sites (≤2, >2), lines of Tx for MBC (≤2, >2), and CTX choice (capecitabine, eribulin, gemcitabine, or vinorelbine). Sequential primary end points were central-blinded review of PFS and OS.Results: The intent-to-treat (ITT) population comprised 536 pts (M, 266; T, 270). At the median follow-up of 20.2 mo among all ITT pts, pts received a median of 7 cycles of M + CTX vs 6 cycles of T + CTX. Median OS after 385 events in the ITT population was 21.6 mo with M vs 21.9 mo with T (HR .95; 95% CI .77-1.17; P=.62; Table). Based on a prespecified, non-α-allocated exploratory analysis, a numerical OS advantage in favor of the M arm was observed in the subgroup of pts homozygous for the CD16A-158F low-affinity allele (median OS, 23.6 vs 19.2 mo; HR .72; 95% CI .52-1.00; nominal P=.05). In contrast, in the small subgroup of CD16A-158V homozygotes, median OS was longer for T vs M (31.1 mo vs 22.0 mo; HR 1.77; 95% CI 1.01-3.12; nominal P=.04). Grade ≥3 adverse events (AE) occurred in 146 pts (55.3%) receiving M vs 141 pts (53.0%) receiving T. Serious AEs were seen in 47 pts (17.8%) receiving M vs 51 pts (19.2%) receiving T. Incidence of infusion-related reactions was higher with M (36 [13.6%]) vs T (9 [3.4%]). Left ventricular dysfunction requiring delay or cessation of M/T administration occurred in 4 pts (1.5%) receiving M and in 7 pts (2.6%) receiving T. Conclusions: The median OS in the ITT population was not statistically different between the 2 arms. An exploratory analysis of CD16A genotyping indicates a numerical OS advantage in favor of M in F homozygous pts, along with a numerical OS advantage in favor of T in V homozygous pts. Safety of M + CTX was similar to previous reports and consistent with M FDA-approved label. Studies of M in HER2+ breast cancer pts with different CD16A allelic variants are warranted, including MARGOT, the neoadjuvant investigator-initiated study on the efficacy of M vs T in pts carrying F-allelic variants of CD16A. Median OSITT analysisPrespecified, non-α-allocated exploratory analysis (n=506)N=536CD16A-158F carriers (F/F and F/V)(n=437)CD16A-158F homozygotes (F/F)(n=192)CD16A-158F/V heterozygotes(n=245)CD16A-158V homozygotes (V/V)(n=69)aM + CTX, mo21.6 (n=266)23.3 (n=221)23.6 (n=102)21.3 (n=119)22.0 (n=37)T + CTX, mo21.9 (n=270)20.8 (n=216)19.2 (n=90)22.0 (n=126)31.1 (n=32)HR (95% CI)0.95 (0.77-1.17)0.86 (0.69-1.08)0.72 (0.52-1.00)0.96 (0.71-1.30)1.77 (1.01-3.12)P value0.620.19b0.05b0.78b0.04bAbbreviations: CTX, chemotherapy; HR, hazard ratio; ITT, intent to treat; M, margetuximab; mo, months; OS, overall survival; T, trastuzumab. Cutoff date: June 14, 2021. aThis subgroup was characterized by an imbalance in poor prognostic features. bNominal P value. Citation Format: Hope Rugo, Seock-Ah Im, Fatima Cardoso, Javier Cortes, Giuseppe Curigliano, Antonino Musolino, Mark D. Pegram, Thomas Bachelot, Gail S. Wright, Cristina Saura, Santiago Escrivá-de-Romaní, Michelino De Laurentiis, Gary N. Schwartz, Timothy Pluard, Francesco Ricci, William Gwin, III, Christelle Levy, Ursa Brown-Glaberman, Jean-Marc Ferrero, Maaike de Boer, Sung-Bae Kim, Katarína Petráková, Denise A. Yardley, Orit Freedman, Erik H. Jakobsen, Einav Nili Gal-Yam, Rinat Yerushalmi, Peter A. Fasching, Emily Ashley, Shengyan Hong, Minori Rosales, William J. Gradishar. Phase 3 SOPHIA study of margetuximab (M) + chemotherapy (CTX) vs trastuzumab (T) + CTX in patients (pts) with HER2+ metastatic breast cancer (MBC) after prior anti-HER2 therapies: Final overall survival (OS) analysis [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD8-01.

Background This randomised, double-blind study compared PF-05280014 (a trastuzumab biosimilar) with reference trastuzumab (Herceptin®) sourced from the European Union (trastuzumab-EU), when each was given with paclitaxel as first-line treatment for HER2-positive metastatic breast cancer. Methods Between 4 April 2014 and 22 January 2016, 707 participants were randomised 1:1 to receive intravenous PF-05280014 plus paclitaxel (PF-05280014 group; n = 352) or trastuzumab-EU plus paclitaxel (trastuzumab-EU group; n = 355). PF-05280014 or trastuzumab-EU was administered weekly (first dose 4 mg/kg, subsequent doses 2 mg/kg), with the option to change to a 3-weekly regimen (6 mg/kg) from Week 33. Treatment with PF-05280014 or trastuzumab-EU could continue until disease progression. Paclitaxel (starting dose 80 mg/m2) was administered on Days 1, 8 and 15 of 28-day cycles for at least six cycles or until maximal benefit of response. The primary endpoint was objective response rate (ORR), evaluating responses achieved by Week 25 and confirmed by Week 33, based on blinded central radiology review. Results The risk ratio for ORR was 0.940 (95% CI: 0.842–1.049). The 95% CI fell within the pre-specified equivalence margin of 0.80–1.25. ORR was 62.5% (95% CI: 57.2–67.6%) in the PF-05280014 group and 66.5% (95% CI: 61.3–71.4%) in the trastuzumab-EU group. As of data cut-off on 11 January 2017 (using data up to 378 days post-randomisation), there were no notable differences between groups in progression-free survival (median: 12.16 months in the PF-05280014 group vs. 12.06 months in the trastuzumab-EU group; 1-year rate: 54% vs. 51%) or overall survival (median: not reached in either group; 1-year rate: 89.31% vs. 87.36%). Safety outcomes and immunogenicity were similar between the treatment groups. Conclusion When given as first-line treatment for HER2-positive metastatic breast cancer, PF-05280014 plus paclitaxel demonstrated equivalence to trastuzumab-EU plus paclitaxel in terms of ORR. CLINICAL TRIAL REGISTRATION ClinicalTrials.gov, NCT01989676

Metastatic breast cancer continues to be a life-threatening diagnosis that impacts hundreds of thousands of patients around the world. Targeted therapies are usually associated with less toxicity compared with cytotoxic chemotherapies and often induce response or durable disease control in estrogen receptor (ER) and/or HER2+ breast cancers. Drugs that target CDK 4/6 either alone or in combination with endocrine therapy have demonstrated substantial improvements in progression-free survival (PFS) compared with endocrine monotherapy. Most recently, PARP inhibitors have shown longer PFS compared with physician’s choice of chemotherapy in BRCA-associated cancers, leading to the first U.S. Food and Drug Administration (FDA) approval of a targeted therapy with the potential to benefit a subgroup of patients with triple-negative breast cancer (TNBC). Finally, newer drug delivery strategies using antibody drug conjugates have also allowed a “targeted approach” to deliver moderate to extremely potent cytotoxins directly to sites of metastatic disease, with less toxicity.

Background: To date, anti-HER2 monoclonal antibodies are the only immune therapies approved for treating pts with HER2-over-expressing cancers. Intratumoral delivery of immunostimulatory adjuncts such as toll-like receptor (TLR) 7/8 agonists can activate tumor resident antigen-presenting cells (APCs) to promote antitumor immunity. To optimize intratumoral delivery while leveraging favorable preclinical biology we developed a novel, systemically delivered ISAC (BDC-1001). BDC-1001 consists of an investigational trastuzumab biosimilar chemically conjugated to a TLR 7/8 agonist (payload) with an intervening non-cleavable linker. BDC-1001 activates human myeloid APCs and retains antibody-mediated effector functions such as antibody-dependent cellular cytotoxicity/phagocytosis. Our trastuzumab-based ISACs seem to elicit potent and durable immune-mediated antitumor efficacy including tumor regression in a TLR- and Fc receptor-dependent manner in xenograft and syngeneic tumor resistant models (Ackerman et al. Nat Cancer 2020). BDC-1001 did not induce interstitial lung disease, cytokine release syndrome, or thrombocytopenia in non-human primate studies. A four-part phase 1/2, first-in-human study was initiated in 2020 to evaluate BDC-1001 with or without (±) pembro in pts with HER2-overexpressing or amplified advanced solid tumors. Methods: This phase 1/2 dose-escalation/expansion study will enroll up to 390 pts with HER2-overexpressing (IHC2+ or 3+) or HER2-amplified (by in situ hybridization or next-generation sequencing) advanced solid tumors. Patients may have received prior anti-HER2 therapies. Primary objectives of dose-escalation are safety and tolerability, and establishing a recommended phase 2 dose of BDC-1001 alone administered IV q3w (Part 1) and combined with pembro (Part 2). Primary endpoints of Parts 1 & 2 include assessment of safety and tolerability; dose-limiting immune-related toxicities in a 3+3 design. The dose-expansion phase 2 portion will evaluate preliminary antitumor activity of BDC-1001 alone (Part 3) and with pembro (Part 4) using RECIST v1.1 and iRECIST. The primary endpoint of the phase 2 is best\ overall response rate; with secondary endpoints of duration of response, disease control rate, and progression-free survival. Exploratory objectives include pharmacokinetic parameters and pharmacodynamic biomarkers associated with drug exposure to help elucidate mechanism of action and identify biomarkers to improve selection of pts most likely to benefit from the single therapy or combination. Recruitment is ongoing (NCT04278144). Citation Format: Manish R. Sharma, Richard D. Carvajal, Daniel Catenacci, Leisha A. Emens, Glenn J. Hanna, Dejan Juric, Yoon-Koo Kang, Jeeyun Lee, Keun-Wook Lee, Bob T. Li, Kathleen Moore, Mark D. Pegram, Paula R. Pohlmann, Drew Rasco, Alexander Spira, Arielle L. Heeke, Ding Wang, Lawrence Garbo, Sudhir Manda, Jasgit Sachdev, Shelley E. Ackerman, Heidi LeBlanc, David Dornan, Marcin Kowanetz, Michael N. Alonso, Amreen Husain, Edith A. Perez, Ecaterina Ileana Dumbrava. Phase 1/2 study of a novel HER2 targeting TLR7/8 immune-stimulating antibody conjugate (ISAC), BDC-1001, alone and in combination with pembrolizumab (pembro) in patients (pts) with HER2-expressing advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT218.

Introduction: The irreversible pan-HER inhibitor NER showed modest single agent activity for HER2mut MBC in Part I of MutHER trial. In Part II, we hypothesized that (1) N+F would improve activity in estrogen receptor positive (ER+) HER2mut MBC due to ER-HER2 crosstalk and (2) dual HER2 blockade by adding trastuzumab at disease progression (PD) could overcome resistance. Methods: Pts with ER+HER2mut MBC were enrolled to 2 cohorts (FUL treated or naive) to receive N+F with diarrhea prophylaxis. ER- pts received NER in an exploratory ER- cohort. Trastuzumab was added at PD if approved by insurance. Simon's Minimax 2-stage phase II design with the primary endpoint of clinical benefit rate (CBR: rates of complete/partial response [CR/PR] plus stable disease [SD] >24 weeks [wks]), with anticipated vs null hypothesis being CBR of 55% vs 35% (FUL treated) or 65% vs 40% (FUL naïve) with 80% power, 1 sided 0.05 alpha, was used. Secondary endpoints included progression free survival (PFS) and adverse events (AEs). Serial blood samples were analyzed for circulating tumor DNA (ctDNA) by Guardant360 for concomitant mutations, HER2mut variant allele frequency (VAF) dynamics, and resistance mechanisms. Results: Between Sep. 2015 and Oct. 2020, 40 pts with HER2mut MBC were enrolled, completing the 1st stage of each ER+ cohort. 35 pts (21 FUL treated, 10 FUL naïve, 4 ER-) were evaluable for response, with median age 63 (35-82) years, 3 (0-12) prior MBC regimen, lobular BC in 13 (37%) and visceral mets in 32 (91%) pts. 21 (68%) ER+ pts had prior CDK4/6 inhibitor. All but 1 pt has come off study due to PD. Table 1 shows the efficacy by cohort. Further enrollment is closed per protocol. Adding trastuzumab at PD induced CB in 4 (3 PR, 1 SD≥24 wks) of 5 pts (1 ER-, 4 ER+), with PFS 28 (95% CI 18~NA) wks. Common AEs across cohorts were diarrhea (G3 21%) and fatigue (G3 5%). No G4 AEs. ctDNA HER2mut was detected in 72% (23/32) baseline (BL) samples tested. In pts with paired samples, HER2mut VAF decreased at C1D15/C2D1 from BL in 75% (15/20) and rose in 89% (16/18) at PD. Acquired HER2mut, including the T798I gatekeeper mutation, were detected in 2 pts at PD. Mutations in TP53 (53%), PIK3CA (43%), and CDH1 (35%) were common, but none significantly associated with PFS in all or ER+ pts. Conclusions: NER, or N+F, is active for HER2mut MBC with good tolerability. Adding trastuzumab at PD induced further response, supporting dual HER2 blockade for HER2mut MBC. Table 1.EfficacyCohortFUL treatedFUL naïveER-Best Response, n evaluablen = 21n = 10n = 4CR, n100PR, n431SD (≥ 24 wks), n300SD (< 24 wks), n1030PD, n343CBR, n with CB/total n evaluable, % (95% CI)8 of 20*, 40% (19~64%)3 of 10, 30% (7~65%)1 of 4, 25% (0.6~81%)mPFS (95% CI), wks, ITT (n)24 (16~31) wks, (n = 24)20 (8~NA) wks, (n = 11)8.5 (8~NA) wks, (n = 5)*20 of 21 pts are evaluable for CBR in the FUL treated Cohort as 1 pt had SD as best response and treatment is still ongoing. ITT (intent to treat) population is used for mPFS estimate. Citation Format: Cynthia X. Ma, Jingqin Luo, Rachel A. Freedman, Timothy Pluard, Julie Nangia, Janice Lu, Frances Valdez-Albini, Melody Cobleigh, Jason Jones, Nancy U. Lin, Eric Winer, P. Kelly Marcom, Shana Thomas, Jill Anderson, Brittney Haas, Kimberly M. Hamann, Richard Bryce, Alshad S. Lalani, Lisa Carey, Matthew Goetz, Feng Gao, Gretchen Kimmick, Mark Pegram, Matthew J. Ellis, Ron Bose. A phase II trial of neratinib (NER) or NER plus fulvestrant (FUL) (N+F) in HER2 mutant, non-amplified (HER2mut) metastatic breast cancer (MBC): Part II of MutHER [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT026.

Purpose: Based on promising preclinical data, we conducted a single-arm phase II trial to assess the clinical benefit rate (CBR) of neratinib, defined as complete/partial response (CR/PR) or stable disease (SD) ≥24 weeks, in HER2mut nonamplified metastatic breast cancer (MBC). Secondary endpoints included progression-free survival (PFS), toxicity, and circulating tumor DNA (ctDNA) HER2mut detection. Experimental Design: Tumor tissue positive for HER2mut was required for eligibility. Neratinib was administered 240 mg daily with prophylactic loperamide. ctDNA sequencing was performed retrospectively for 54 patients (14 positive and 40 negative for tumor HER2mut). Results: Nine of 381 tumors (2.4%) sequenced centrally harbored HER2mut (lobular 7.8% vs. ductal 1.6%; P = 0.026). Thirteen additional HER2mut cases were identified locally. Twenty-one of these 22 HER2mut cases were estrogen receptor positive. Sixteen patients [median age 58 (31–74) years and three (2–10) prior metastatic regimens] received neratinib. The CBR was 31% [90% confidence interval (CI), 13%–55%], including one CR, one PR, and three SD ≥24 weeks. Median PFS was 16 (90% CI, 8–31) weeks. Diarrhea (grade 2, 44%; grade 3, 25%) was the most common adverse event. Baseline ctDNA sequencing identified the same HER2mut in 11 of 14 tumor-positive cases (sensitivity, 79%; 90% CI, 53%–94%) and correctly assigned 32 of 32 informative negative cases (specificity, 100%; 90% CI, 91%–100%). In addition, ctDNA HER2mut variant allele frequency decreased in nine of 11 paired samples at week 4, followed by an increase upon progression. Conclusions: Neratinib is active in HER2mut, nonamplified MBC. ctDNA sequencing offers a noninvasive strategy to identify patients with HER2mut cancers for clinical trial participation. Clin Cancer Res; 23(19); 5687–95. ©2017 AACR.

Summary Background The antibody–drug conjugate trastuzumab emtansine is indicated for the treatment of patients with HER2-positive metastatic breast cancer previously treated with trastuzumab and a taxane. Approval of this drug was based on progression-free survival and interim overall survival data from the phase 3 EMILIA study. In this report, we present a descriptive analysis of the final overall survival data from that trial. Methods EMILIA was a randomised, international, open-label, phase 3 study of men and women aged 18 years or older with HER2-positive unresectable, locally advanced or metastatic breast cancer previously treated with trastuzumab and a taxane. Enrolled patients were randomly assigned (1:1) via a hierarchical, dynamic randomisation scheme and an interactive voice response system to trastuzumab emtansine (3·6 mg/kg intravenously every 3 weeks) or control (capecitabine 1000 mg/m 2 self-administered orally twice daily on days 1–14 on each 21-day cycle, plus lapatinib 1250 mg orally once daily on days 1–21). Randomisation was stratified by world region (USA vs western Europe vs or other), number of previous chemotherapy regimens for unresectable, locally advanced, or metastatic disease (0 or 1 vs >1), and disease involvement (visceral vs non-visceral). The coprimary efficacy endpoints were progression-free survival (per independent review committee assessment) and overall survival. Efficacy was analysed in the intention-to-treat population; safety was analysed in all patients who received at least one dose of study treatment, with patients analysed according to the treatment actually received. On May 30, 2012, the study protocol was amended to allow crossover from control to trastuzumab emtansine after the second interim overall survival analysis crossed the prespecified overall survival efficacy boundary. This study is registered with ClinicalTrials.gov, number NCT00829166. Findings Between Feb 23, 2009, and Oct 13, 2011, 991 eligible patients were enrolled and randomly assigned to either trastuzumab emtansine (n=495) or capecitabine and lapatinib (control; n=496). In this final descriptive analysis, median overall survival was longer with trastuzumab emtansine than with control (29·9 months [95% CI 26·3–34·1] vs 25·9 months [95% CI 22·7–28·3]; hazard ratio 0·75 [95% CI 0·64–0·88]). 136 (27%) of 496 patients crossed over from control to trastuzumab emtansine after the second interim overall survival analysis (median follow-up duration 24·1 months [IQR 19·5–26·1]). Of those patients originally randomly assigned to trastuzumab emtansine, 254 (51%) of 495 received capecitabine and 241 [49%] of 495 received lapatinib (separately or in combination) after study drug discontinuation. In the safety population (488 patients treated with capecitabine plus lapatinib, 490 patients treated with trastuzumab emtansine), fewer grade 3 or worse adverse events occurred with trastuzumab emtansine (233 [48%] of 490) than with capecitabine plus lapatinib control treatment (291 [60%] of 488). In the control group, the most frequently reported grade 3 or worse adverse events were diarrhoea (103 [21%] of 488 patients) followed by palmar–plantar erythrodysaesthesia syndrome (87 [18%]), and vomiting (24 [5%]). The safety profile of trastuzumab emtansine was similar to that reported previously; the most frequently reported grade 3 or worse adverse events in the trastuzumab emtansine group were thrombocytopenia (70 [14%] of 490), increased aspartate aminotransferase levels (22 [5%]), and anaemia (19 [4%]). Nine patients died from adverse events; five of these deaths were judged to be related to treatment (two in the control group [coronary artery disease and multiorgan failure] and three in the trastuzumab emtansine group [metabolic encephalopathy, neutropenic sepsis, and acute myeloid leukaemia]). Interpretation This descriptive analysis of final overall survival in the EMILIA trial shows that trastuzumab emtansine improved overall survival in patients with previously treated HER2-positive metastatic breast cancer even in the presence of crossover treatment. The safety profile was similar to that reported in previous analyses, reaffirming trastuzumab emtansine as an efficacious and tolerable treatment in this patient population. Funding F Hoffmann-La Roche/Genentech.

Background: Human epidermal growth factor receptor 2 (HER2)-targeting monoclonal antibodies (mAb) are the standard of care in early-to-advanced HER2+ breast cancer. However, for relapsed/refractory disease, limited options exist after progression on trastuzumab (T), pertuzumab (P), and ado-trastuzumab emtansine. Margetuximab (M) is an Fc-engineered anti-HER2 mAb that targets the same epitope as T and exerts similar antiproliferative effects. Compared with T, M has higher affinity for both 158V (high binding) and 158F (low binding) alleles of the activating Fc receptor, CD16A. M enhances innate immunity, including CD16A-mediated antibody-dependent cellular cytotoxicity, more effectively than T. M also potentiates adaptive immunity in treated patients (pts), including enhanced clonality of the T-cell repertoire and induction of HER2-specific T- and B-cell responses. SOPHIA (NCT02492711) is a phase 3 trial that demonstrated the benefit of M vs T, both with chemotherapy, in pts with HER2+ metastatic breast cancer (MBC). This trial is the first prospective analysis of the effect of CD16A genotype on anti-HER2 antibody efficacy. Methods: Pts with disease progression after at least 2 lines of anti-HER2 therapy, including P, and 1-3 lines of therapy for HER2+ MBC were randomized 1:1 to chemotherapy + either M (15 mg/kg intravenously every 3 wk) or T. Randomization was stratified by number of metastatic sites (≤2, >2), lines of treatment for MBC (≤2, >2), and chemotherapy choice (capecitabine, eribulin, gemcitabine, or vinorelbine). Primary endpoints were central-blinded review of progression-free survival (PFS) and overall survival (OS). The first interim OS analysis at time of PFS analysis (October 10, 2018) was immature, with 158 of 385 deaths (41%) needed for final OS analysis. The stopping boundary was not crossed. A second interim OS analysis was planned after 270 deaths and will be reported here. Results: The intent-to-treat (ITT) population comprised 536 pts (M, 266; H, 270). M + chemotherapy prolonged PFS vs T + chemotherapy (median PFS, 5.8 vs 4.9 mo; hazard ratio [HR], 0.76; 95% confidence interval [CI]: 0.59-0.98; P=0.033). Results were more pronounced in pts with CD16A genotypes containing a 158F allele (median PFS, 6.9 vs 5.1 mo; HR, 0.68; 95% CI: 0.52-0.90; nominal P=0.005). OS at the first interim analysis demonstrated a HR (95% CI) of 0.95 (0.69-1.31) for the ITT population (n=536) and an HR of 0.82 (95% CI: 0.58-1.17) for the CD16A/FF or FV genotype population (n=457). Grade ≥3 adverse events (AEs) occurred in 138 pts (52%) receiving M vs 128 pts (48%) receiving T. Serious AEs were seen in 39 (15%) receiving M vs 46 (17%) receiving T. The second planned interim analysis of OS (at n=270), as well as updated safety, will be presented. Conclusions: M + chemotherapy in pts with treated HER2+ MBC improves PFS vs T. Safety was comparable. CD16A genotyping suggests a greater benefit in pts with a 158F allele. Maturing data comparing the OS of pts treated with M vs T with chemotherapy will provide important new insights in characterizing clinical activity of this regimen in pts with MBC. Citation Format: Hope S. Rugo, Seock-Ah Im, Fatima Cardoso, Javier Cortes, Giuseppe Curigliano, Mark D. Pegram, Antonino Musolino, Thomas Bachelot, Gail S. Wright, Michelino De Laurentiis, Peter A. Kaufman, Timothy Pluard, Francesco Ricci, Lupe G. Salazar, Denise A. Yardley, Sutton Edlich, Shengyan Hong, Edwin Rock, William J. Gradishar, SOPHIA Study Group. Phase 3 SOPHIA study of margetuximab + chemotherapy vs trastuzumab + chemotherapy in patients with HER2+ metastatic breast cancer after prior anti-HER2 therapies: second interim overall survival analysis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr GS1-02.

Background We assessed long-term cardiac safety and efficacy in patients with human epidermal growth factor receptor 2–positive early breast cancer treated with a trastuzumab biosimilar (SB3) or its reference product, trastuzumab (TRZ), in a phase 3 study. Methods Patients who completed the phase 3 study could be enrolled in this extension study. The outcomes included the incidence of symptomatic congestive heart failure (CHF), asymptomatic significant left ventricular ejection fraction (LVEF) decrease, incidence of other cardiac events, event-free survival (EFS), and overall survival. In post hoc analysis, the Cox proportional hazards regression model was used to assess factors associated with EFS. Results A total of 367 patients were enrolled in the study (SB3, n = 186; TRZ, n = 181). The median follow-up duration from the main study enrolment was 40.8 and 40.5 months for SB3 and TRZ, respectively. During the two-year follow-up after adjuvant therapy, incidence of asymptomatic significant LVEF decrease was rare (SB3, n = 1; TRZ, n = 2), with all patients recovering with LVEF ≥ 50%, and no cases of symptomatic CHF or other cardiac events were reported. At 3 years, the EFS was 91.9% with SB3 and 85.2% with TRZ. The number of patients with events was 17 (9.1%) with SB3 and 31 (17.1%) with TRZ [hazard ratio: 0.47, 95% confidence interval: 0.26–0.87]. Antibody-dependent cell-mediated cytotoxicity (ADCC) activity and the breast pathologic complete response rate were the factors associated with EFS. Conclusion Cardiotoxicity was rare in this extension study. EFS was higher with SB3 versus TRZ, with post hoc analysis suggesting that a downward drift in ADCC activity was a contributing factor. Clinical trial registration numbers NCT02771795 (EudraCT 2015-005663-17).

1043 Background: Tucatinib (TUC) is an oral tyrosine kinase inhibitor (TKI) highly specific for HER2. TUC is approved for use in combination with trastuzumab (T) and capecitabine (C) in patients (pts) with and without brain metastases (BM) who have received 1 or more prior anti-HER2–based regimens in the metastatic setting. In the primary analysis from the pivotal HER2CLIMB trial, the addition of TUC to T and C in pts with HER2+ metastatic breast cancer showed a statistically significant and clinically meaningful prolongation of progression-free (PFS) (HR = 0.54 [95% CI: 0.42, 0.71]; P < 0.001) and overall survival (OS) (HR = 0.66 [95% CI: 0.50, 0.88]; P = 0.005) (Murthy, et al. NEJM 2020). TUC in combination with T and C was well tolerated with few discontinuations other than for disease progression. Based on these data, the protocol was amended for unblinding of sites to treatment assignment to allow for crossover from the placebo arm to receive TUC in combination with T and C. Methods: HER2CLIMB (NCT02614794) is a global, randomized, double-blind, placebo-controlled trial in pts with unresectable locally advanced or metastatic HER2+ breast cancer previously treated with T, pertuzumab, and T-emtansine (T-DM1), including pts with untreated, treated stable, or treated and progressing BM. Overall 612 pts were randomized 2:1 to receive TUC 300 mg BID or placebo, each in combination with T and C. Randomization was stratified by BM, ECOG performance status, and geographic region. Protocol prespecified analysis of OS, PFS (by investigator assessment) and safety in the total study population will be performed at approximately 2 years from the last patient randomized. Results: Updated Kaplan-Meier time-to-event analysis of OS and PFS with hazard ratios and 95% confidence intervals for TUC arm vs placebo arm will be presented overall, as well as for OS in the prespecified subgroups reported previously (Murthy, et al. NEJM 2020). Safety and tolerability assessments will include frequency of adverse events by severity, dose modifications and discontinuation of study medications. Conclusions: Conclusions will be presented in the presentation. Clinical trial information: NCT02614794 .

1063 Background: Rintodestrant, a potent, oral selective estrogen receptor degrader, competitively binds and degrades the estrogen receptor (ER), thus blocking ER signaling in tumors resistant to other endocrine therapies (ET). Results from parts 1 and 2 dose-escalation/expansion indicate that once-daily (QD) rintodestrant has a favorable safety profile and antitumor activity in patients (pts) with heavily pretreated ER+/HER2– advanced breast cancer (ABC), including those with ESR1 variants (Aftimos et al. SABCS 2020 [PS12-04, PD8-07]). The optimal dose of rintodestrant was 800 mg. Here, we present part 3, combining rintodestrant with the CDK4/6 inhibitor palbociclib. Methods: This open-label study evaluated rintodestrant in pts with ER+/HER2– ABC after progression on ET (NCT03455270). Part 3 assessed rintodestrant 800 mg QD + palbociclib 125 mg QD for 21 days every 28 days. Key eligibility criteria included ≤1 line of chemotherapy and/or ≤1 line of ET in the advanced setting, with ≥6 months of ET in the advanced setting and/or ≥24 months in the adjuvant setting. Prior CDK4/6 inhibitor therapy was not allowed. Primary objectives included safety and efficacy. Secondary objectives included pharmacokinetics and antitumor activity (RECIST v1.1). Exploratory objectives included mutation profiling (cell-free DNA) at baseline and cycle 1 day 15. Results: Enrollment occurred Jul–Oct 2020. As of Dec 9, 2020, 40 pts were treated, with a median age of 58 years (35–76) and ECOG PS of 0 (70%) or 1 (30%); 20% had de novo stage 4 disease, 10% bone-only, and 68% visceral metastases. Median number of visceral sites was 1 (0–3): 30% of pts with lung and 40% with liver involvement. Median number of prior lines in the advanced setting was 1 (0–2), including chemotherapy (48%), fulvestrant (15%), and aromatase inhibitors (50%). Most recent ET was given in the adjuvant and metastatic settings in 28% and 73% of pts, respectively. Rintodestrant-related adverse events (AEs) were reported in 8% of pts—all nonserious and grade 2—and included nausea (3%), vomiting (3%), and neutropenia (3%). The most common (≥10%) treatment-related AEs (rintodestrant and/or palbociclib) were neutropenia (88%), leukopenia (45%), anemia (10%), and thrombocytopenia (10%); grade 3/4 neutropenia was 38%/15%, in line with the safety profile of palbociclib. No deaths or treatment discontinuations due to AEs were reported. At data cutoff (median treatment duration of 3 months [1.5–4.6]), 28 pts (70%) remained on study treatment, 2 (5%) had a confirmed partial response, and 27 (68%) had stable disease. Additional efficacy and pharmacodynamic data will be presented. Conclusions: Rintodestrant, as monotherapy or combined with palbociclib, continues to demonstrate an excellent safety/tolerability profile with promising antitumor activity in pts with ER+/HER2– ABC, including those with ESR1 variants. Clinical trial information: NCT03455270 .