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Purpose: Praluzatamab ravtansine (CX-2009) is a conditionally activated Probody drug conjugate (PDC) comprising an anti-CD166 mAb conjugated to DM4, with a protease-cleavable linker and a peptide mask that limits target engagement in normal tissue and circulation. The tumor microenvironment is enriched for proteases capable of cleaving the linker, thereby releasing the mask, allowing for localized binding of CX-2009 to CD166. CX-2009 was evaluated in a phase I/II clinical trial for patients with advanced solid tumors. Patients and Methods: Eligible patients had metastatic cancer receiving ≥2 prior treatments. CX-2009 was administered at escalating doses every 3 weeks (0.25–10 mg/kg) or every 2 weeks (4–6 mg/kg). Primary objective was to determine the safety profile and recommended phase II dose (RP2D). Results: Of 99 patients enrolled, the most prevalent subtype was breast cancer (n = 45). Median number of prior therapies was 5 (range, 1–19). Dose-limiting toxicities were observed at 8 mg/kg every 3 weeks and 6 mg/kg every 2 weeks. On the basis of tolerability, the RP2D was 7 mg/kg every 3 weeks. Tumor regressions were observed at doses ≥4 mg/kg. In the hormone receptor–positive/HER2-nonamplified breast cancer subset (n = 22), 2 patients (9%) had confirmed partial responses, and 10 patients (45%) had stable disease. Imaging with zirconium-labeled CX-2009 confirmed uptake in tumor lesions and shielding of major organs. Activated, unmasked CX-2009 was measurable in 18 of 22 posttreatment biopsies. Conclusions: CD166 is a novel, ubiquitously expressed target. CX-2009 is the first conditionally activated antibody–drug conjugate to CD166 to demonstrate both translational and clinical activity in a variety of tumor types.

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Pharmacokinetics: Z-endoxifen levels per taselisib dose level

Purpose:The strategy of combining endocrine therapy with PI3K-mTOR inhibition has shown promise in estrogen receptor (ER)–positive breast cancer, but new agents and combinations with a better therapeutic index are urgently needed. Taselisib is a potent, selective, beta-isoform–sparing PI3 kinase inhibitor.Patients and Methods:30 patients with ER-positive, metastatic breast cancer who had failed prior endocrine therapy were treated with escalating doses of taselisib (2 or 4 mg in an intermittent or continuous schedule) combined with tamoxifen 20 mg once daily in this phase 1b study using a “rolling six” design.Results:Taselisib combined with tamoxifen was generally well tolerated, with treatment-emergent adverse events as expected for this class of drugs, including diarrhea (13 patients, 43%), mucositis (10 patients, 33%), and hyperglycemia (8 patients, 27%). No dose-limiting toxicities were observed. Objective responses were seen in 6 of 25 patients with RECIST-measurable disease (ORR 24%). Median time to disease progression was 3.7 months. Twelve of 30 patients (40%) had disease control for 6 months or more. Circulating tumor (ct)DNA studies using next-generation tagged amplicon sequencing identified early indications of treatment response and mechanistically relevant correlates of clinical drug resistance (e.g., mutations in KRAS, ERBB2) in some patients.Conclusions:Taselisib can be safely combined with tamoxifen at the recommended phase 2 dose of 4 mg given once daily on a continuous schedule. Preliminary evidence of antitumor activity was seen in both PIK3CA mutant and wild-type cancers. The randomized phase 2 part of POSEIDON (testing tamoxifen plus taselisib or placebo) is currently recruiting.

Purpose:PROCLAIM-CX-2029 is a phase I first-in-human study of CX-2029, a Probody–drug conjugate targeting CD71 (transferrin receptor 1) in adults with advanced solid tumors. Although the transferrin receptor is highly expressed across multiple tumor types, it has not been considered a target for antibody–drug conjugates (ADCs) due to its broad expression on normal cells. CX-2029 is a masked form of a proprietary anti-CD71 antibody conjugated to monomethyl auristatin E, designed to be unmasked in the tumor microenvironment by tumor-associated proteases, therefore limiting off-tumor toxicity and creating a therapeutic window for this previously undruggable target.Patients and Methods:This was a dose-escalation, multicenter trial to evaluate the safety, pharmacokinetics, pharmacodynamics, and antitumor activity of CX-2029. The primary endpoint was to determine the maximum tolerated dose (MTD) and cycle 1 dose-limiting toxicity (DLT). CX-2029 was administered i.v. every 3 weeks.Results:Forty-five patients were enrolled in eight dose levels. No DLTs were reported in the dose escalation through 4 mg/kg. At 5 mg/kg, there were two DLTs (febrile neutropenia and pancytopenia). Following expansion of the 4 mg/kg dose to six patients, two additional DLTs were observed (infusion-related reaction and neutropenia/anemia). Both the 4 and 5 mg/kg doses were declared above the maximum tolerated dose. The recommended phase II dose is 3 mg/kg. The most common dose-dependent hematologic toxicities were anemia and neutropenia. Confirmed partial responses were observed in three patients, all with squamous histologies.Conclusions:The Probody therapeutic platform enables targeting CD71, a previously undruggable ADC target, at tolerable doses associated with clinical activity.See related commentary by Oberoi and Garralda, p. 4459

Supplementary Methods Text

Plots of reticulocyte percentages from Cycle 1 Day 1 through Cycle 2 Day 1

Supplementary Data from Praluzatamab Ravtansine, a CD166-Targeting Antibody–Drug Conjugate, in Patients with Advanced Solid Tumors: An Open-Label Phase I/II Trial

Purpose:Praluzatamab ravtansine (CX-2009) is a conditionally activated Probody drug conjugate (PDC) comprising an anti-CD166 mAb conjugated to DM4, with a protease-cleavable linker and a peptide mask that limits target engagement in normal tissue and circulation. The tumor microenvironment is enriched for proteases capable of cleaving the linker, thereby releasing the mask, allowing for localized binding of CX-2009 to CD166. CX-2009 was evaluated in a phase I/II clinical trial for patients with advanced solid tumors.Patients and Methods:Eligible patients had metastatic cancer receiving ≥2 prior treatments. CX-2009 was administered at escalating doses every 3 weeks (0.25–10 mg/kg) or every 2 weeks (4–6 mg/kg). Primary objective was to determine the safety profile and recommended phase II dose (RP2D).Results:Of 99 patients enrolled, the most prevalent subtype was breast cancer (n = 45). Median number of prior therapies was 5 (range, 1–19). Dose-limiting toxicities were observed at 8 mg/kg every 3 weeks and 6 mg/kg every 2 weeks. On the basis of tolerability, the RP2D was 7 mg/kg every 3 weeks. Tumor regressions were observed at doses ≥4 mg/kg. In the hormone receptor–positive/HER2-nonamplified breast cancer subset (n = 22), 2 patients (9%) had confirmed partial responses, and 10 patients (45%) had stable disease. Imaging with zirconium-labeled CX-2009 confirmed uptake in tumor lesions and shielding of major organs. Activated, unmasked CX-2009 was measurable in 18 of 22 posttreatment biopsies.Conclusions:CD166 is a novel, ubiquitously expressed target. CX-2009 is the first conditionally activated antibody–drug conjugate to CD166 to demonstrate both translational and clinical activity in a variety of tumor types.

Background: SERENA-1 (NCT03616587) is a Phase 1, multi-part, open-label study of camizestrant in women with ER+/HER2− advanced breast cancer. Parts A/B and C/D (escalation/expansion) examined camizestrant as monotherapy and in combination with palbociclib respectively and have been presented previously.1,2 Here we present data from parts G/H which examined camizestrant in combination with abemaciclib. Methods: The primary objective was to determine the safety and tolerability of camizestrant 75 mg once daily (QD) in combination with abemaciclib 150 mg twice daily (BID). Secondary objectives included investigation of anti-tumor response and pharmacokinetics (PK). Participants were previously treated women of any menopausal status (pre-menopausal women received this combination alongside ongoing ovarian function suppressors). Prior treatment with ≤2 lines of chemotherapy in the advanced setting was permitted. There was no limit on the number of lines of prior endocrine treatment in the advanced setting; previous treatment with CDK4/6 inhibitors (CDK4/6i) and fulvestrant was permitted. Results: As of 1st June 2022, 24 patients had received camizestrant in combination with abemaciclib with a median 7.7 month follow up. Tolerability of the combination of camizestrant and abemaciclib was consistent with that of each drug individually. No patient required camizestrant dose reduction. All camizestrant-related heart rate decreases were Grade 1 (asymptomatic). PK data for camizestrant in combination with abemaciclib were consistent with camizestrant as monotherapy and published abemaciclib steady-state PK data, indicating no clinically relevant drug-drug interaction. In these heavily pre-treated patients (46% prior chemotherapy, 75% prior CDK4/6i, 54% prior fulvestrant; all in the advanced disease setting) and of whom 67% had visceral metastases, the objective response rate was 5/19 (26.3%), the clinical benefit rate at 24 weeks was 16/24 (66.7%) and the median progression-free survival had not been reached, with 8/24 patients experiencing a progression event. These data support the use of camizestrant 75 mg QD combined with the approved abemaciclib dose. Conclusions: Camizestrant 75 mg QD in combination with abemaciclib 150 mg BID was well tolerated with encouraging clinical activity. The inclusion of this regimen in the ongoing Phase 3, SERENA-6 trial 3, of camizestrant combined with CDK4/6i versus an aromatase inhibitor, will further clarify the role of this combination in the treatment of patients with ER+/HER2− advanced breast cancer with tumors expressing ESR1 mutations. References 1. Baird R, Oliveira M, Ciruelos Gil EM, et al. SABCS 2020 Virtual Meeting. Abstract PS11-05. 2. Oliveira M, Hamilton EP, Incorvati J, et al. J Clin Oncol 40, 2022 (suppl 16; abstr 1032). 3. SERENA-6 trial. Available at https://clinicaltrials.gov/ct2/show/NCT04964934 We acknowledge Helen Heffron, PhD, from InterComm International who provided medical writing support funded by AstraZeneca. Citation Format: Nicholas Turner, Christos Vaklavas, Emiliano Calvo, Javier Garcia-Corbacho, Jason Incorvati, Manuel Ruiz Borrego, Chris Twelves, Anne Armstrong, Begoña Bermejo, Erika Hamilton, Mafalda Oliveira, Eva Ciruelos, Peter Kabos, Manish R Patel, Maria Borrell, Howard Burris, Bruno de Paula, Alejandro Falcon, Cristina Hernando, Irene Moreno, Ciara S. O’Brien, Elena Shagisultanova, Ivan Victoria Ruiz, Judy S. Wang, Mei Wei, Tim Brier, Danielle Carroll, Carmela Ciardullo, Lisa Gibbons, itziar irurzun-Arana, Tony Jack, bistra kirova, Teresa Klinowska, Justin Lindemann, Julie Maidment, Alastair Mathewson, Rhiannon Maudsley, Robert McEwen, Christopher Morrow, Andy Sykes, Richard D. Baird. SERENA-1: Updated analyses from a Phase 1 study of the next generation oral selective estrogen receptor degrader camizestrant (AZD9833) combined with abemaciclib, in women with ER-positive, HER2-negative advanced breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-07-28.

Purpose: PROCLAIM-CX-2029 is a phase I first-in-human study of CX-2029, a Probody–drug conjugate targeting CD71 (transferrin receptor 1) in adults with advanced solid tumors. Although the transferrin receptor is highly expressed across multiple tumor types, it has not been considered a target for antibody–drug conjugates (ADCs) due to its broad expression on normal cells. CX-2029 is a masked form of a proprietary anti-CD71 antibody conjugated to monomethyl auristatin E, designed to be unmasked in the tumor microenvironment by tumor-associated proteases, therefore limiting off-tumor toxicity and creating a therapeutic window for this previously undruggable target. Patients and Methods: This was a dose-escalation, multicenter trial to evaluate the safety, pharmacokinetics, pharmacodynamics, and antitumor activity of CX-2029. The primary endpoint was to determine the maximum tolerated dose (MTD) and cycle 1 dose-limiting toxicity (DLT). CX-2029 was administered i.v. every 3 weeks. Results: Forty-five patients were enrolled in eight dose levels. No DLTs were reported in the dose escalation through 4 mg/kg. At 5 mg/kg, there were two DLTs (febrile neutropenia and pancytopenia). Following expansion of the 4 mg/kg dose to six patients, two additional DLTs were observed (infusion-related reaction and neutropenia/anemia). Both the 4 and 5 mg/kg doses were declared above the maximum tolerated dose. The recommended phase II dose is 3 mg/kg. The most common dose-dependent hematologic toxicities were anemia and neutropenia. Confirmed partial responses were observed in three patients, all with squamous histologies. Conclusions: The Probody therapeutic platform enables targeting CD71, a previously undruggable ADC target, at tolerable doses associated with clinical activity. See related commentary by Oberoi and Garralda, p. 4459

Background: Triple-negative breast cancer (TNBC) is associated with poor survival outcomes and treatment options are limited. These tumors lack therapeutic targets and become rapidly resistant to chemotherapy. The anti–PD-1 antibody pembrolizumab showed durable antitumor activity and manageable safety in patients with TNBC in the KEYNOTE-012, KEYNOTE-086, and KEYNOTE-119 studies. The combination of lenvatinib, an antiangiogenic multiple receptor tyrosine kinase inhibitor, with pembrolizumab has shown promising clinical outcomes in early-phase clinical trials across several cancer types. LEAP-005 (ClinicalTrials.gov, NCT03797326) is an ongoing study evaluating the efficacy and safety of lenvatinib combined with pembrolizumab in patients with previously treated advanced solid tumors. Here, we report the first results from the TNBC cohort of LEAP-005. Methods: This ongoing, multicohort, open-label, phase 2 study enrolled patients aged ≥18 y with previously treated, histologically or cytologically confirmed advanced TNBC. PD-L1 expression was assessed at a central laboratory using the PD-L1 IHC 22C3 pharmDx assay and measured using the combined positive score (CPS; number of PD-L1–positive tumor cells, lymphocytes, and macrophages divided by total number of tumor cells x 100). Patients received lenvatinib 20 mg once daily orally plus pembrolizumab 200 mg every 3 weeks intravenously for a maximum of 35 pembrolizumab doses, then lenvatinib alone until progressive disease or unacceptable toxicity. Primary endpoints were objective response rate (ORR) by blinded independent central review per RECIST version 1.1 and safety. Key secondary endpoints were disease control rate (DCR; defined as best overall response of complete response [CR], partial response [PR], or stable disease [SD] per RECIST v1.1), duration of response (DOR), progression-free survival (PFS), and overall survival (OS). Safety was monitored through 30 days after the last dose of study drug (90 days for serious AEs), with AEs graded using NCI CTCAE v4.0. Results: 31 patients have been enrolled in the TNBC cohort of LEAP-005. Median age was 56 y (range, 37 to 85), 58% had received ≥2 prior lines of therapy, and 26% had CPS ≥10 tumors. As of the April 10, 2020 data cutoff, median follow-up was 7 mo (range, 4 to 13). ORR was 29% (95% CI: 14–48), with 1 CR and 8 PRs. 9 pts had SD, and the DCR (CR + PR + SD) was 58% (95% CI: 39–76). 4 responses (1 CR and 3 PRs) were in patients with CPS ≥10 tumors (n=8) for an ORR of 50% (95% CI: 16–84), and 5 responses (all PRs) were in patients with CPS Citation Format: Hyun Cheol Chung, Esma Saada-Bouzid, Federico Longo Muñoz, Eduardo Yanez, Seock-Ah Im, Eduardo Castanon, Donna M. Graham, Javier Garcia-Corbacho, Juanita Lopez, Razi Ghori, Corina Dutcus, Alan Smith, Kevin Norwood, Carlos Gomez-Roca. Lenvatinib plus pembrolizumab for previously treated, advanced triple-negative breast cancer: Early results from the multicohort phase 2 LEAP-005 study [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 PS12-07.

Background: AZD9833 is an oral selective estrogen receptor (ER) antagonist and degrader (SERD) in Phase 2 clinical development for the treatment of ER+ HER2− breast cancer. Here we report data from Parts C and D of the ongoing Phase 1 study (SERENA-1) examining AZD9833 in combination with palbociclib, together with updated data from Parts A and B examining AZD9833 monotherapy. Methods: SERENA-1 (NCT03616587) is an ongoing open-label Phase 1 study of AZD9833 in pre- and post-menopausal women with ER+, HER2− advanced breast cancer who have previously received ≥1 endocrine therapy and ≤2 prior chemotherapies. Prior treatment with fulvestrant and/or CDK4/6 inhibitors was permitted. The primary objective is to determine the safety and tolerability of once daily (QD) AZD9833, with dose-limiting toxicities (DLTs) in the first 28 days defining the maximum tolerated dose. Secondary objectives include anti-tumor response (including circulating tumor [ct] DNA response) and pharmacokinetics. Parts A (escalation) and B (expansion) assess AZD9833 as a monotherapy, and Parts C (escalation) and D (expansion) assess AZD9833 in combination with palbociclib. Results: At a data cut-off of March 24 2020, 17 patients had received either 150 mg or 300 mg AZD9833 in combination with palbociclib, given according to its product labeling. Eighty patients had received AZD9833 monotherapy at doses of 25, 75, 150, 300, and 450 mg QD. In patients treated with AZD9833 and palbociclib, treatment-related adverse events (AEs; experienced by ≥10% of patients) included visual disturbances*, bradycardia*, asthenia, anemia, QTcF prolongation, nausea, neutropenia, decreased white blood cell count, and vomiting (*combined terms). All instances of AZD9833-related bradycardia were Grade 1. One DLT was observed in the 150 mg cohort: CTCAE Grade 2 visual disturbances, which began on Cycle 1 Day 8 and resolved by Cycle 1 Day 9 following dose interruption. The patient restarted treatment on Cycle 1 Day 15 at 75 mg and continued this dose until data cut-off. No causally related AEs led to discontinuation of AZD9833. The tolerability of AZD9833 with palbociclib was consistent with the observed tolerability profile of AZD9833 monotherapy, and the known tolerability profile of palbociclib. Pharmacokinetic analysis showed similar AZD9833 exposure for monotherapy and palbociclib combination therapy. Similarly, palbociclib exposure was comparable with simulations using a published population pharmacokinetic model. In Part A, ESR1 hotspot mutations were detected in ctDNA at baseline in 26/56 (46%) patients; 13/26 (50%) of these patients achieved a partial response or stable disease at 24 weeks, including 5/10 (50%) with a Y537S ESR1 mutation. Further, in patients with ESR1 mutations and samples available for longitudinal ctDNA analysis, 17/20 (85%) exhibited a reduction or loss of mutant ESR1 on treatment with AZD9833. Efficacy data to be presented include objective response rate and clinical benefit rate at 24 weeks. Of note, unconfirmed partial responses have been observed in Part C after the data cut-off for this abstract. Conclusions: AZD9833 continues to show an encouraging efficacy and dose-dependent safety profile as a monotherapy or in combination with palbociclib. A Phase 2 study comparing the efficacy and safety of three doses of AZD9833 versus fulvestrant (NCT04214288), and a Phase 2 pre-surgical ‘window of opportunity’ study (EUDRA-CT; 2019-003706-2) are ongoing. Citation Format: Richard Baird, Mafalda Oliveira, Eva Maria Ciruelos Gil, Manish R Patel, Begoña Bermejo de las Heras, Manuel Ruiz-Borrego, Javier García-Corbacho, Anne Armstrong, Udai Banerji, Chris Twelves, Valentina Boni, Jason Incorvati, Peter Kabos, Adam L Cohen, Bruno de Paula, Marta Capelán Rodríguez, Judy S Wang, Christina Hernando, Alejandro Falcón Gonzalez, Ivan Victoria Ruiz, Julia Lai-Kwon, Anosheh Afghani, Christos Vaklavas, Tim Brier, Steven Fox, Bistra Kirova, Teresa Klinowska, Chris Leach, Justin PO Lindemann, Richard Mather, Rhiannon Maudsley, Christopher J Morrow, Nitharsan Sathiyayogan, Andy Sykes, Li Zhang, Erika Hamilton. Updated data from SERENA-1: A Phase 1 dose escalation and expansion study of the next generation oral SERD AZD9833 as a monotherapy and in combination with palbociclib, in women with ER-positive, HER2-negative advanced 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 PS11-05.

Background: Insulin-like growth factor receptor-1 (IGF-1R) signaling is implicated in cancer progression, prognosis, and treatment resistance. Cross-talk between IGF-1R signaling and cyclin-dependent kinase (CDK) 4 & 6 was reported in preclinical studies, and synergy was shown with concurrent inhibition of IGF-1R signaling and CDK 4 & 6. The CDK 4 & 6 inhibitor, abemaciclib, is FDA approved for hormone receptor-positive [HR+], HER2- advanced BC (ABC) in combination with an aromatase inhibitor as initial endocrine-based therapy, with fulvestrant for progression following endocrine therapy (ET), and as monotherapy for progression following ET and prior chemotherapy in the metastatic setting. NCT03099174 is a prospective, open-label study investigating the safety and tolerability of concurrent inhibition of IGF/IGF-1R signaling with the IGF-1/2-neutralizing monoclonal antibody, xentuzumab, plus abemaciclib (provided by Eli Lilly), with or without ET. Methods: 4 dose-finding cohorts were evaluated in 2 parts using a Bayesian Logistic Regression Model with overdose control, fitted to toxicity outcomes. Part 1 (Cohort A) included pts with solid tumors who had failed/were intolerant of prior treatments, or had no other option available. The starting dose was xentuzumab 1000 mg i.v. weekly plus abemaciclib 150 mg orally (p.o.) every 12 h (Q12h). Part 1 determined the maximum tolerated dose (MTD) and/or recommended phase II dose (RP2D) prior to starting Part 2. Part 2 included postmenopausal women with HR+, HER2- BC who had received 0-2 prior lines of chemotherapy in the metastatic setting and were eligible for ET. One of 3 ETs was combined with xentuzumab plus abemaciclib (doses determined in Part 1): Cohort B, letrozole; Cohort C, anastrozole; Cohort D, fulvestrant. Previous CDK 4 & 6 inhibitor therapy was not permitted. Treatment was given until progression, lack of tolerability, or withdrawal. Primary endpoints were MTD and dose-limiting toxicities (DLTs) during the first 28-day cycle. Tumor response and progression-free survival (PFS) were also assessed. Results: 27 pts were treated (26 female [96.3%]; median age, 58 years [range 34-70]); 9 pts remained on treatment at the time of analysis. Cohorts A/B/C/D included 6/7/6/8 pts. Cohort A included pts with ABC (n=3), and lung cancer, sarcoma, and colorectal cancer (n=1 each). In total, 23 pts were evaluable for MTD. MTD was xentuzumab 1000 mg i.v. weekly plus abemaciclib 150 mg p.o. Q12h in Cohorts A, B, and D (Cohort C is ongoing). During Cycle 1, 4 DLTs were reported (Cohort A: grade 3 neutrophil count decrease, n=1; Cohort B: grade 3 neutrophil count decrease, n=1; Cohort C: grade 4 thrombocytopenia, n=1; Cohort D: grade 3 neutropenia, n=1). The most common drug-related AEs (DRAEs) in Cohort A were diarrhea and decreased appetite (66.7% each), and nausea, vomiting, and asthenia (50% each). The most common DRAEs in Cohorts B/C/D were diarrhea (90.5%), asthenia (66.7%), anemia (61.9%), neutropenia (57.1%), and nausea (52.4%). Most were reversible and grade 1/2. The most common grade 3/4 DRAEs were diarrhea (16.7/0%) in Cohort A, and neutropenia (19.0/14.3%) and diarrhea (14.3/0%) in Cohorts B/C/D. 4 pts had a best overall response of partial response (Cohorts A and B, n=1; Cohort D, n=2) and 10 pts had stable disease (Cohort A/B/C/D, n=1/3/1/5; duration currently Citation Format: Douglas Yee, Mafalda Oliveira, Hiroji Iwata, Anthony Gonçalves, Javier García-Corbacho, Marie Paule Sablin, Aleix Prat, Molly Catherine Hardebeck, Marta Puig, Dennis Chin-Lun Huang, Mingchi Hsu, Patricia LoRusso. A phase Ib multi-cohort study of xentuzumab and abemaciclib in patients (pts) with solid tumors and breast cancer (BC) - Initial report of four dose-finding cohorts [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 P3-11-05.

Current evidence suggests that plasma cell-free DNA (cfDNA) is fragmented around a mode of 166 bp. Data supporting this view has been mainly acquired through the analysis of double-stranded cfDNA. The characteristics and diagnostic potential of single-stranded and damaged double-stranded cfDNA in healthy individuals and cancer patients remain unclear. Here, through a combination of high-affinity magnetic bead–based DNA extraction and single-stranded DNA sequencing library preparation (MB-ssDNA), we report the discovery of a large proportion of cfDNA fragments centered at ∼50 bp. We show that these “ultrashort” cfDNA fragments have a greater relative abundance in plasma of healthy individuals (median = 19.1% of all sequenced cfDNA fragments, n = 28) than in plasma of patients with cancer (median = 14.2%, n = 21, P < 0.0001). The ultrashort cfDNA fragments map to accessible chromatin regions of blood cells, particularly in promoter regions with the potential to adopt G-quadruplex (G4) DNA secondary structures. G4-positive promoter chromatin accessibility is significantly enriched in ultrashort plasma cfDNA fragments from healthy individuals relative to patients with cancers (P < 0.0001), in whom G4-cfDNA enrichment is inversely associated with copy number aberration-inferred tumor fractions. Our findings redraw the landscape of cfDNA fragmentation by identifying and characterizing a novel population of ultrashort plasma cfDNA fragments. Sequencing of MB-ssDNA libraries could facilitate the characterization of gene regulatory regions and DNA secondary structures via liquid biopsy. Our data underline the diagnostic potential of ultrashort cfDNA through classification for cancer patients.

BackgroundProbody®therapeutics are antibody prodrugs that are activated in the tumor microenvironment by tumor-associated proteases, thereby restricting the activity to the tumor microenvironment and minimizing ‘off-tumor’ toxicity. We report dose-escalation and single-agent expansion phase data from the first-in-human study of CX-072 (pacmilimab), a Probody checkpoint inhibitor directed against programmed death-ligand 1 (PD-L1).MethodsIn the dose-escalation phase of this multicenter, open-label study (NCT03013491), adults with advanced solid tumors (naive to programmed-death-1/PD-L1 or cytotoxic T-lymphocyte-associated antigen 4 inhibitors) were enrolled into one of seven dose-escalation cohorts, with pacmilimab administered intravenously every 14 days. The primary endpoints were safety and determination of the maximum tolerated dose (MTD). In the expansion phase, patients with one of six prespecified malignancies (triple-negative breast cancer [TNBC]; anal squamous cell carcinoma [aSCC]; cutaneous SCC [cSCC]; undifferentiated pleomorphic sarcoma [UPS]; small bowel adenocarcinoma [SBA]; and thymic epithelial tumor [TET]); or high tumor mutational burden (hTMB) tumors were enrolled. The primary endpoint was objective response (Response Evaluation Criteria In Solid Tumors v.1.1).ResultsAn MTD was not reached with doses up to 30 mg/kg. A recommended phase 2 dose (RP2D) of 10 mg/kg was chosen based on pharmacokinetic and pharmacodynamic findings in the expansion phase. Ninety-eight patients enrolled in the expansion phase: TNBC (n=14), aSCC (n=14), cSCC (n=14), UPS (n=20), SBA (n=14), TET (n=8), and hTMB tumors (n=14). Of 114 patients receiving pacmilimab at the RP2D, grade ≥3 treatment-related adverse events (TRAEs) were reported in 10 patients (9%), serious TRAEs in six patients (5%), and treatment discontinuation due to TRAEs in two patients (2%). Grade ≥3 immune-related AEs occurred in two patients (rash, myocarditis). High PD-L1 expression (ie, >50% Tumor Proportion Score) was observed in 22/144 (19%) patients. Confirmed objective responses were observed in patients with cSCC (n=5, including one complete response), hTMB (n=4, including one complete response), aSCC (n=2), TNBC (n=1), UPS (n=1), and anaplastic thyroid cancer (n=1).ConclusionsPacmilimab can be administered safely at the RP2D of 10 mg/kg every 14 days. At this dose, pacmilimab had a low rate of immune-mediated toxicity and showed signs of antitumor activity in patients not selected for high PD-L1 expression.Trial registration numberNCT03013491.

Background Probody® therapeutics are antibody prodrugs that are activated in the tumor microenvironment by tumor-associated proteases, thereby restricting the activity to the tumor microenvironment and minimizing ‘off-tumor’ toxicity. We report dose-escalation and single-agent expansion phase data from the first-in-human study of CX-072 (pacmilimab), a Probody checkpoint inhibitor directed against programmed death-ligand 1 (PD-L1). Methods In the dose-escalation phase of this multicenter, open-label study (NCT03013491), adults with advanced solid tumors (naive to programmed-death-1/PD-L1 or cytotoxic T-lymphocyte-associated antigen 4 inhibitors) were enrolled into one of seven dose-escalation cohorts, with pacmilimab administered intravenously every 14 days. The primary endpoints were safety and determination of the maximum tolerated dose (MTD). In the expansion phase, patients with one of six prespecified malignancies (triple-negative breast cancer [TNBC]; anal squamous cell carcinoma [aSCC]; cutaneous SCC [cSCC]; undifferentiated pleomorphic sarcoma [UPS]; small bowel adenocarcinoma [SBA]; and thymic epithelial tumor [TET]); or high tumor mutational burden (hTMB) tumors were enrolled. The primary endpoint was objective response (Response Evaluation Criteria In Solid Tumors v.1.1). Results An MTD was not reached with doses up to 30 mg/kg. A recommended phase 2 dose (RP2D) of 10 mg/kg was chosen based on pharmacokinetic and pharmacodynamic findings in the expansion phase. Ninety-eight patients enrolled in the expansion phase: TNBC (n=14), aSCC (n=14), cSCC (n=14), UPS (n=20), SBA (n=14), TET (n=8), and hTMB tumors (n=14). Of 114 patients receiving pacmilimab at the RP2D, grade ≥3 treatment-related adverse events (TRAEs) were reported in 10 patients (9%), serious TRAEs in six patients (5%), and treatment discontinuation due to TRAEs in two patients (2%). Grade ≥3 immune-related AEs occurred in two patients (rash, myocarditis). High PD-L1 expression (ie, >50% Tumor Proportion Score) was observed in 22/144 (19%) patients. Confirmed objective responses were observed in patients with cSCC (n=5, including one complete response), hTMB (n=4, including one complete response), aSCC (n=2), TNBC (n=1), UPS (n=1), and anaplastic thyroid cancer (n=1). Conclusions Pacmilimab can be administered safely at the RP2D of 10 mg/kg every 14 days. At this dose, pacmilimab had a low rate of immune-mediated toxicity and showed signs of antitumor activity in patients not selected for high PD-L1 expression. Trial registration number NCT03013491.

BackgroundProbody® therapeutics are antibody prodrugs designed to be activated by tumor-associated proteases. This conditional activation restricts antibody binding to the tumor microenvironment, thereby minimizing ‘off-tumor’ toxicity. Here, we report the phase 1 data from the first-in-human study of CX-072 (pacmilimab), a Probody immune checkpoint inhibitor directed against programmed death-ligand 1 (PD-L1), in combination with the anti-cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA-4) antibody ipilimumab.MethodsAdults (n=27) with advanced solid tumors (naive to PD-L1/programmed cell death protein 1 or CTLA-4 inhibitors) were enrolled in the phase 1 combination therapy dose-escalation portion of this multicenter, open-label, phase 1/2 study (NCT03013491). Dose-escalation pacmilimab/ipilimumab followed a standard 3+3 design and continued until the maximum tolerated dose (MTD) was determined. Pacmilimab+ipilimumab was administered intravenously every 3 weeks for four cycles, followed by pacmilimab administered every 2 weeks as monotherapy. The primary objective was identification of dose-limiting toxicities and determination of the MTD. Other endpoints included the rate of objective response (Response Evaluation Criteria In Solid Tumors v.1.1).ResultsTwenty-seven patients were enrolled in pacmilimab (mg/kg)+ipilimumab (mg/kg) dose-escalation cohorts: 0.3+3 (n=6); 1+3 (n=3); 3+3 (n=3); 10+3 (n=8); 10+6 (n=6); and 10+10 (n=1). Dose-limiting toxicities occurred in three patients, one at the 0.3+3 dose level (grade 3 dyspnea/pneumonitis) and two at the 10+6 dose level (grade 3 colitis, grade 3 increased aspartate aminotransferase). The MTD and recommended phase 2 dose was pacmilimab 10 mg/kg+ipilimumab 3 mg/kg administered every 3 weeks. Pacmilimab-related grade 3–4 adverse events (AEs) and grade 3–4 immune-related AEs were reported in nine (33%) and six (22%) patients, respectively. Three patients (11%) discontinued treatment because of AEs. The overall response rate was 19% (95% CI 6.3 to 38.1), with one complete (anal squamous cell carcinoma) and four partial responses (cancer of unknown primary, leiomyosarcoma, mesothelioma, testicular cancer). Responses lasted for >12 months in four patients.ConclusionsThe MTD and recommended phase 2 dose of pacmilimab (10 mg/kg)+ipilimumab (3 mg/kg) every 3 weeks is active and has a favorable tolerability profile.

Purpose: The strategy of combining endocrine therapy with PI3K-mTOR inhibition has shown promise in estrogen receptor (ER)–positive breast cancer, but new agents and combinations with a better therapeutic index are urgently needed. Taselisib is a potent, selective, beta-isoform–sparing PI3 kinase inhibitor. Patients and Methods: 30 patients with ER-positive, metastatic breast cancer who had failed prior endocrine therapy were treated with escalating doses of taselisib (2 or 4 mg in an intermittent or continuous schedule) combined with tamoxifen 20 mg once daily in this phase 1b study using a “rolling six” design. Results: Taselisib combined with tamoxifen was generally well tolerated, with treatment-emergent adverse events as expected for this class of drugs, including diarrhea (13 patients, 43%), mucositis (10 patients, 33%), and hyperglycemia (8 patients, 27%). No dose-limiting toxicities were observed. Objective responses were seen in 6 of 25 patients with RECIST-measurable disease (ORR 24%). Median time to disease progression was 3.7 months. Twelve of 30 patients (40%) had disease control for 6 months or more. Circulating tumor (ct)DNA studies using next-generation tagged amplicon sequencing identified early indications of treatment response and mechanistically relevant correlates of clinical drug resistance (e.g., mutations in KRAS, ERBB2) in some patients. Conclusions: Taselisib can be safely combined with tamoxifen at the recommended phase 2 dose of 4 mg given once daily on a continuous schedule. Preliminary evidence of antitumor activity was seen in both PIK3CA mutant and wild-type cancers. The randomized phase 2 part of POSEIDON (testing tamoxifen plus taselisib or placebo) is currently recruiting.

IMPORTANCE: Therapies targeting the programmed cell death 1 (PD-1) receptor or its ligand (PD-L1), such as the humanized monoclonal antibody durvalumab, have shown durable clinical responses in several tumor types. However, concerns about the safety and feasibility of PD-1/PD-L1 blockade in HIV-1-infected individuals have led to the exclusion of these patients from clinical trials on cancer immunotherapies. OBJECTIVE: To evaluate the feasibility and safety of durvalumab treatment in patients with advanced cancer and virologically controlled HIV-1 infection. DESIGN, SETTING, AND PARTICIPANTS: The DURVAST study was a nonrandomized, open-label, phase 2 clinical trial in patients with any solid tumor type in which anti-PD-1 or anti-PD-L1 antibodies have approved indications or for which there are data of antitumoral activity with no other available curative therapy. All patients had basal undetectable plasma viremia while undergoing combination antiretroviral therapy. INTERVENTIONS: Treatment consisted of intravenous infusion of durvalumab (1500 mg every 4 weeks) until disease progression or unacceptable toxic effects. MAIN OUTCOMES AND MEASURES: Adverse events were graded with the use of the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.03. Tumor response was evaluated using the Response Evaluation Criteria in Solid Tumors version 1.1. RESULTS: A total of 20 HIV-1-infected patients with advanced cancer were enrolled; 16 (80%) were male, the median (range) age was 54 (30-73) years, and 12 (60%) had progressed with previous cancer treatment lines. A median (range) of 4 (1-16) cycles of durvalumab were administered. Drug-related adverse events were observed in 50% of patients, and all were grade 1 and 2 (mainly diarrhea, asthenia, and arthromyalgia). Four of 16 response-evaluable patients (25%) had a partial response. Five patients (31%) had stable disease, including 4 with durable stable disease (disease control rate of 50%). CD4+ and CD8+ T-cell counts and plasma HIV-1 viremia remained stable throughout the study. CONCLUSIONS AND RELEVANCE: Durvalumab treatment was feasible and safe in HIV-1-infected patients with cancer receiving combination antiretroviral therapy. HIV-1-infected patients on suppressive antiretroviral therapy with advanced cancer should have access to cancer immunotherapy treatments. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03094286.

Background Epertinib (S-222611) is a potent reversible inhibitor of HER2, EGFR and HER4. This trial evaluated the safety, tolerability, pharmacokinetics and antitumour activity of daily oral epertinib combined with trastuzumab (arm A), with trastuzumab plus vinorelbine (arm B) or with trastuzumab plus capecitabine (arm C), in patients with HER2-positive metastatic breast cancer (MBC). Methods Eligible patients, with or without brain metastases, had received prior HER2-directed therapy. A dose-escalation phase determined the tolerability of each combination and established a dose for further study. Further, patients were recruited to expansion cohorts in each of the 3 arms to further explore efficacy and safety. Results The recommended doses of epertinib were 600 mg, 200 mg and 400 mg in arms A, B and C, respectively. The most frequent grade 3/4 adverse event (AE) was diarrhoea in all arms, which was manageable with medical intervention and dose modification. The objective response rate (complete response [CR] plus partial response [PR]) in heavily pre-treated HER2-positive MBC patients at the recommended doses of epertinib combined with trastuzumab was 67% (N = 9), with trastuzumab plus vinorelbine was 0% (N = 5) and with trastuzumab plus capecitabine was 56% (N = 9). Notably, 4 of 6 patients previously treated with T-DM1 responded in the arm A expansion cohort (epertinib plus trastuzumab). In the arm C expansion cohort (epertinib plus trastuzumab plus capecitabine), 4 of 7 patients responded despite previous exposure to capecitabine. Measurable regression of brain metastases was observed in patients with CNS target lesions treated in both arms A and C. Conclusion We observed safety, tolerability and encouraging antitumour activity of epertinib combined with trastuzumab, or with trastuzumab plus capecitabine. This supports further evaluation of these combinations in patients with pre-treated HER2-positive MBC, with or without brain metastases. Trial registration EudraCT Number: 2013-003894-87; registered 09-September-2013.

3564 Background: Pembrolizumab (pembro), an anti-PD-1 antibody, is approved for the treatment of patients (pts) with unresectable or metastatic microsatellite instability-high (MSI-H) or mismatch repair (MMR) deficient colorectal cancer, both as first-line treatment and after progression following treatment with fluoropyrimidine, oxaliplatin, and irinotecan. The combination of lenvatinib, a multiple receptor tyrosine kinase inhibitor, and anti-PD-1 treatment showed synergistic antitumor activity in preclinical models. LEAP-005 (NCT03797326) is evaluating the efficacy and safety of lenvatinib plus pembro in pts with previously treated advanced solid tumors. We present findings from the colorectal cancer cohort. Methods: In this nonrandomized, open-label, phase 2 study, adult pts (aged ≥18 y) with histologically/cytologically documented metastatic and/or unresectable colorectal cancer, non–MSI-H/pMMR tumor per local determination, previous treatment with oxaliplatin and irinotecan in separate lines of therapy, measurable disease per RECIST v1.1, ECOG PS of 0‒1, and a tissue sample evaluable for PD-L1 expression were eligible. Pts received lenvatinib 20 mg QD plus pembro 200 mg Q3W for up to 35 cycles of pembro (̃2 y) or until confirmed disease progression, unacceptable toxicity, or withdrawal of consent. Treatment with lenvatinib could continue beyond 2 y in pts with clinical benefit. Primary endpoints were ORR (per RECIST v1.1 by blinded independent central review) and safety. Secondary endpoints included disease control rate (DCR), duration of response (DOR), PFS, and OS. Tumor imaging was performed Q9W from treatment initiation for 54 wks, then Q12W to week 102, and Q24W thereafter. Results: 32 pts with colorectal cancer received treatment with lenvatinib plus pembro (median age, 56 y [range, 36-77]; male, 81%; 3L, 91%); median time from first dose to data cutoff (April 10, 2020) was 10.6 mo (range, 5.9-13.1). ORR was 22% (95% CI, 9–40; table). Grade 3–5 treatment-related AEs occurred in 16 (50%) pts. Treatment-related AEs led to treatment discontinuation in 3 pts (grade 2 ischemic stroke [n = 1], grade 3 increased liver transaminases [n = 1], grade 5 intestinal perforation [n = 1]). Conclusions: In pts with previously treated advanced non–MSI-H/pMMR colorectal cancer, lenvatinib plus pembro demonstrated promising antitumor activity and a manageable safety profile. Enrollment in the colorectal cohort was expanded to 100 pts. Clinical trial information: NCT03797326. [Table: see text]

3060 Background: Genetic profiling (GP) is essential not only for understanding tumor biology but also helps to identify potential genes for targeted therapies. At the same time, selected CT provide an individual genomic profile panel during the pre-screening phase. Here, we demonstrate our experience using these panels. Methods: We selected 14 CT from our Early Drug Development Clinical Trial Unit at Hospital Clinic of Barcelona that included analysis of gene panels in tumor (Foundation One, ArcherDX, Therascreen and Sophia Genetics) or plasma (Resolution Bioscience ctDx). These panels analyzed mutations, fusions, amplifications, microsatellite instability (MSI) and tumor mutational burden (TMB), among others. We collected information about types of cancers, molecular alterations and therapies chosen according to the results of GP. The platform OncoKB (Chakravarty JCO PO, 2017) was used to define genes with potential target therapies and levels of evidence (LE) for those targets (from LE 1 –FDA-recognized biomarker predictive of response to an FDA-approved drug- to LE 4 –Compelling biological evidence supports the biomarker as being predictive of response to a drug). Descriptive statistics were used. Results: From March 2017 to January 2021 we analyzed samples from 410 patients (pts) with CNS (19.3%), urothelial (18.3%), prostate (17.6%), breast (15.4%), ovarian (9.3%), esophageal and gastric (5.4%), colorectal (4.4%), pancreas (2.7%), endometrial (2.4%), cholangiocarcinoma (1.2%), cervix (1%), HNSCC (1%), renal (1%), lung (0.5%), liver (0.2%) fallopian tube (0.2%) and paraganglioma (0.2%). 352 pts (85.8%) had at least 1 genetic alteration. The most frequently altered genes were TP53 (153 pts, 46.2%), INSR (19 pts, 22.8%), TERT (76 pts, 22%), CDKN2A (65 pts, 19.9%), FAM175A (11 pts, 19.3%), CDKN2B (54 pts, 18.1%), MLL2 (53 pts, 17.7%), PTEN (52 pts, 16%), MTAP (45 pts, 15.7%), PIK3CA (52 pts, 15%) and ATM (55 pts, 14.4%). TMB ranged from 0 to 76.9 mut/Mb (median 2.5 mut/Mb). MSI was found in 3 pts (1.5%). 196 pts (47.1%) had an OncoKB LE 1 alteration, 105 pts (25.6%) if we restrict the options to their specific cancer type. 16 pts (3.9%) received a matched therapy: 6 pts received an off-label drug, 6 pts were included in the same CT for which the pre-screening was performed and 4 pts were included in a different CT. Additionally, 13 pts (3.2%) received a matched therapy either with OncoKB LE 4 (5 pts received an off-label drug and 3 were included in a different CT) or not included in OncoKB (8 pts included in the same CT of the pre-screening). As a whole, 29 pts (7.1%) received a matched drug according to their genomic results. Conclusions: Comprehensive gene panel testing offered through CT allows the identification of targets to enroll pts, although the recruitment was 1.5%. However, 7.1% of the pts received a matched therapy due to the molecular information of these gene panels.

4080 Background: Second-line treatment options for patients with biliary tract cancers (BTC) are limited. Lenvatinib, an anti-angiogenic multikinase inhibitor, in combination with the programmed death-1 immune checkpoint inhibitor pembrolizumab, has demonstrated promising antitumor activity with a manageable safety profile in patients with select advanced solid tumors. LEAP-005 (NCT03797326) is evaluating the efficacy and safety of lenvatinib plus pembrolizumab in patients with previously treated advanced solid tumors; here we present results from the BTC cohort of LEAP-005. Methods: In this nonrandomized, open-label, phase 2 study, eligible patients were aged ≥18 years with histologically or cytologically documented advanced (metastatic and/or unresectable) BTC with disease progression after 1 prior line of therapy, measurable disease per RECIST v1.1, ECOG PS of 0‒1, and tissue sample evaluable for PD-L1 expression. Patients received lenvatinib 20 mg once daily plus pembrolizumab 200 mg Q3W for up to 35 cycles (approximately 2 years) or until confirmed disease progression, unacceptable toxicity, or withdrawal of consent. Treatment with lenvatinib could continue beyond 2 years in patients experiencing clinical benefit. Primary endpoints were ORR (per RECIST v1.1 by blinded independent central review) and safety. Secondary endpoints were the disease control rate (DCR; comprising CR, PR, and SD), duration of response (DOR), PFS, and OS. Tumor imaging was performed Q9W from treatment initiation for 54 weeks, then Q12W to week 102, and Q24W thereafter. Results: 31 patients were enrolled in the BTC cohort (ECOG PS 1, 55%; 84% ex-US). As of April 10, 2020, median time from first dose to data cutoff (DCO) was 9.5 months (range, 3.1‒11.9), with 8 patients on treatment at DCO. There were 3 (10%) PRs and 18 (58%) SDs. ORR was 10% (95% CI, 2‒26), and DCR was 68% (95% CI, 49‒83). Median DOR was 5.3 months (range, 2.1+ to 6.2). Median PFS was 6.1 months (95% CI, 2.1‒6.4). Median OS was 8.6 months (95% CI, 5.6 to NR). Treatment-related AEs occurred in 30 patients (97%), including 15 (48%) who had grade 3 AEs; there were no grade 4 or 5 treatment-related AEs. 2 (6%) discontinued treatment due to treatment-related AEs (myocarditis, pyrexia; n = 1 each). The most frequent treatment-related AEs were hypertension (42%), dysphonia (39%), diarrhea (32%), fatigue (32%), and nausea (32%). 14 patients (45%) had immune-mediated AEs and 1 patient (3%) had an infusion-related reaction. Conclusions: Lenvatinib plus pembrolizumab demonstrated encouraging efficacy and manageable toxicity in patients with advanced BTC who had received 1 line of prior therapy. Based on these data, enrollment in the BTC cohort has been expanded to 100 patients. Clinical trial information: NCT03797326.

Existing methods to improve detection of circulating tumor DNA (ctDNA) have focused on genomic alterations but have rarely considered the biological properties of plasma cell-free DNA (cfDNA). We hypothesized that differences in fragment lengths of circulating DNA could be exploited to enhance sensitivity for detecting the presence of ctDNA and for noninvasive genomic analysis of cancer. We surveyed ctDNA fragment sizes in 344 plasma samples from 200 patients with cancer using low-pass whole-genome sequencing (0.4×). To establish the size distribution of mutant ctDNA, tumor-guided personalized deep sequencing was performed in 19 patients. We detected enrichment of ctDNA in fragment sizes between 90 and 150 bp and developed methods for in vitro and in silico size selection of these fragments. Selecting fragments between 90 and 150 bp improved detection of tumor DNA, with more than twofold median enrichment in >95% of cases and more than fourfold enrichment in >10% of cases. Analysis of size-selected cfDNA identified clinically actionable mutations and copy number alterations that were otherwise not detected. Identification of plasma samples from patients with advanced cancer was improved by predictive models integrating fragment length and copy number analysis of cfDNA, with area under the curve (AUC) >0.99 compared to AUC 0.91 compared to AUC < 0.5 without fragmentation features. Fragment size analysis and selective sequencing of specific fragment sizes can boost ctDNA detection and could complement or provide an alternative to deeper sequencing of cfDNA.

TPS480 Background: The pan- FGFR tyrosine kinase inhibitor erdafitinib is approved by the US Food and Drug Administration for adults with locally advanced or metastatic urothelial carcinoma and susceptible FGFR3/2 genetic alterations who have progressed during or after ≥ 1 line of prior platinum-containing chemotherapy. FGFR gene alterations are potential oncogenic drivers that have been reported in many solid tumors in adult and pediatric pts. Because of limited response to standard of care options in pts failing systemic therapy, there is strong rationale to assess the safety and efficacy of erdafitinib in adolescent and adult pts with advanced solid tumors and FGFR alterations. Methods: This phase 2, open-label study (RAGNAR/42756493CAN2002; NCT04083976) will include pts aged ≥ 12 years with histologically confirmed unresectable, locally advanced, or metastatic solid tumors (except urothelial tumors) harboring predefined FGFR mutations or fusions. Eligibility screening includes molecular screening for FGFR alterations by central or local next-generation sequencing assays, and other clinical criteria. Pts will enroll into either a broad panel cohort (BPC) of target FGFR alterations or an exploratory cohort (EC) for FGFR alterations that do not meet criteria for BPC. Approximately 280 pts (BPC, n = 240; EC, n = 40) will be enrolled. The primary efficacy end point is overall response rate (ORR) as assessed by the independent review committee. Secondary end points include investigator-assessed ORR, duration of response, disease control rate, progression-free survival, overall survival, safety, pharmacokinetics, and health-related quality of life. Safety assessments include adverse events, vital signs, electrocardiograms, physical examinations, laboratory tests, performance status assessment, growth assessments in adolescents, and ophthalmologic examination. As of December 2019, pts are being enrolled at ~158 sites in 15 countries. Results of this study will provide efficacy and safety data for erdafitinib across multiple solid tumors with FGFR alterations and evaluate the potential benefit of targeting the underlying altered biology of FGFR irrespective of tumor histology in adult and adolescent pts. Clinical trial information: NCT04083976.

321 Background: Second-line treatment options for patients with biliary tract cancers (BTC) are limited. Lenvatinib, an anti-angiogenic multikinase inhibitor, in combination with the programmed death-1 immune checkpoint inhibitor pembrolizumab, has demonstrated promising antitumor activity with a manageable safety profile in patients with select advanced solid tumors. LEAP-005 (NCT03797326) is evaluating the efficacy and safety of lenvatinib plus pembrolizumab in patients with previously treated advanced solid tumors; here we present results from the BTC cohort of LEAP-005. Methods: In this nonrandomized, open-label, phase II study, eligible patients were aged ≥18 years with histologically or cytologically documented advanced (metastatic and/or unresectable) BTC with disease progression after 1 prior line of therapy, measurable disease per RECIST v1.1, ECOG PS of 0‒1, and tissue sample evaluable for PD-L1 expression. Patients received lenvatinib 20 mg once daily plus pembrolizumab 200 mg Q3W for up to 35 cycles (approximately 2 years) or until confirmed disease progression, unacceptable toxicity, or withdrawal of consent. Treatment with lenvatinib could continue beyond 2 years in patients experiencing clinical benefit. Primary endpoints were ORR (per RECIST v1.1 by blinded independent central review) and safety. Secondary endpoints were the disease control rate (DCR; comprising CR, PR, and SD), duration of response (DOR), PFS, and OS. Tumor imaging was performed Q9W from treatment initiation for 54 weeks, then Q12W to week 102, and Q24W thereafter. Results: 31 patients were enrolled in the BTC cohort (ECOG PS 1, 55%; 84% ex-US). As of April 10, 2020, median time from first dose to data cutoff (DCO) was 9.5 months (range, 3.1‒11.9), with 16 patients on treatment at DCO. There were 3 (10%) PRs and 18 (58%) SDs. ORR was 10% (95% CI, 2‒26), and DCR was 68% (95% CI, 49‒83). Median DOR was 5.3 months (range, 2.1+ to 6.2). Median PFS was 6.1 months (95% CI, 2.1‒6.4). Median OS was 8.6 months (95% CI, 5.6 to NR). Treatment-related AEs occurred in 30 patients (97%), including 15 (48%) who had grade 3‒4 AEs; there were no treatment-related deaths. 2 (6%) discontinued treatment due to treatment-related AEs (myocarditis, pyrexia; n = 1 each). The most frequent treatment-related AEs were hypertension (42%), dysphonia (39%), diarrhea (32%), fatigue (32%), and nausea (32%). 14 patients (45%) had immune-mediated AEs and 1 patient (3%) had an infusion-related reaction. Conclusions: Lenvatinib plus pembrolizumab demonstrated encouraging efficacy and manageable toxicity in patients with advanced BTC who had received 1 line of prior therapy. Based on these data, enrollment in the BTC cohort has been expanded to 100 patients. Clinical trial information: NCT03797326.

$\textbf{PURPOSE}$ Limited data are available on cabazitaxel pharmacokinetics in patients with renal impairment. This open-label, multicenter study assessed cabazitaxel in patients with advanced solid tumors and normal or impaired renal function. $\textbf{METHODS}$ Cohorts A (normal renal function: creatinine clearance [CrCL] >80 mL/min/1.73 m$^{2}$), B (moderate renal impairment: CrCL 30 to

Introduction: Treatment with anti PD-1/PD-L1 antibodies has demonstrated clinical activity in different types of solid tumors, but only 20 to 30% of patients (pts) respond to these immune checkpoint inhibitors (ICIs). Therefore, predictive biomarkers of response that can assist in pt selection are urgently needed. Single biomarker expression, like PD-L1, may not provide enough information about cancer cells and the tumor microenviroment. Novel technologies, analyzing hundreds of genes at the same time, are needed to yield better predictive gene signatures of ICI response. The DURVAST trial analyzed the feasibility of durvalumab treatment in HIV-infected cancer pts, which are usually excluded from ICI clinical trials. The trial included 20 patients with different tumor types and yielded a disease control rate of 56%. Methods: Pre-ICI-treatment FFPE tumor tissue samples from 14 HIV-infected cancer pts (including 11 lung, 1 melanoma, 1 anal and 1 bladder cancer) were analyzed using the nCounter NanoString platform with the IO360 panel, including 770 genes involved in tumor biology, microenvironment and immune response. Gene expression results were correlated with clinical benefit (CB) (objective response and stable disease of more than 24 weeks by RECIST1.1 criteria), and compared to other predictive markers. Results: Exploratory analysis of pre-treatment gene expression profiles (GEPs) revealed differentially expressed genes (DEGs) between the pts with- and without CB. Panel-incorporated biological signatures related to tumor and immune activities were evaluated and some of the most DEGs (based on higher log2FC values and nominal p-values ≤0.05) were shown to be involved in cytokine and chemokine signaling. Although not significant, pts without CB tend to have lower expression of genes involved in cytokine and chemokine signaling (p = 0.097). In contrast, pts without CB tended to have a higher TGF beta signature scores (p = 0.318). When combining both signatures, we obtained an aggregated signature score that was significantly different between pts with- and without CB (p = 0.017). While the positive predictive values were the same for all tests, our signature score outperformed PD-L1 expression positivity by immunohistochemistry and PD-L1 RNA expression as predictors for clinical benefit with a two-fold higher sensitivity and negative predictive value. Conclusion: Gene expression analysis of pre-treatment tumor samples revealed distinct GEPs between HIV-infected cancer pts with- and without CB, where combined high baseline recruitment and activation of immune cells by cytokine and chemokine signaling pathways and low immunosuppressive TGF beta signaling pathways predict CB from durvalumab treatment. This predictive score outperformed other predictive markers of CB. These findings need further validation in an external and non-HIV infected pt cohort, in addition to a pt cohort treated with other ICIs. Citation Format: Jillian Wilhelmina Bracht, Maria Gonzalez-Cao, Teresa Moran, Judith Dalmau, Javier Garcia-Corbacho, Reyes Bernabe, Oscar Juan, Javier de Castro, Ana Gimenez-Capitan, Remedios Blanco, Erika Aldeguer, Sonia Rodriguez, Ana Drozdowskyj, Jordi Argilaguet, Julian Blanco, Julia Prado, Christian Brander, Jorge Carrillo, Bonaventura Clotet, Bartomeu Massuti, Mariano Provencio, Chung-Ying Huang, Clara Mayo de las Casas, Monica Garzon, Andres Felipe Cardona, Oscar Arrieta, Andreas Meyerhans, Miguel Angel Molina-Vila, Javier Martinez-Picado, Rafael Rosell. Transcriptomic analysis of pre-treatment tissue samples to predict clinical benefit to durvalumab in HIV-infected cancer patients [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 929.

Introduction: Insulin-like growth factor (IGF) signaling and the cyclin D-cyclin-dependent kinase (CDK) 4 & 6-retinoblastoma pathway are implicated in cancer progression and treatment resistance. Activation of the IGF receptor results in upregulation of cyclin D1 and progression through the cell cycle. Dual inhibition of IGF and CDK 4 & 6 should lead to decreased cell proliferation through disruption of cell-cycle progression. This phase Ib trial assessed safety and preliminary efficacy of xentuzumab, an IGF-ligand neutralizing antibody, in combination with abemaciclib, a CDK 4 & 6 inhibitor. In a dose-finding cohort in patients (pts) with solid tumors, the recommended phase II dose was determined as xentuzumab 1000 mg weekly intravenously plus abemaciclib 150 mg every 12 hours (Q12h) orally. Here, we present data from an expansion cohort in pts with NSCLC. Methods: Eligible pts had stage IV NSCLC with measurable disease which had progressed after platinum-based chemotherapy and immunotherapy, and had either received 1-2 prior chemotherapies for advanced/metastatic disease or were judged ineligible for further standard second-line chemotherapy. Prior CDK 4 & 6 inhibitor therapy was not permitted. Pts received xentuzumab 1000 mg weekly plus abemaciclib 150 mg Q12h until disease progression or intolerability of study medication. The primary endpoint was objective response defined as best overall response of complete response or partial response (PR) per RECIST 1.1. Secondary endpoints included progression-free survival (PFS). Results: 25 pts with NSCLC were treated (17 male [68%], median age 64 years [range 53-76]). 4 pts remained on treatment at time of analysis. Median treatment exposure was 1.6 months (range 0.5-19.7). Of 19 pts evaluable for response, 1 had a best overall response of PR (65% target lesion shrinkage), 9 had stable disease (duration ≥24 weeks in 3 pts) and 9 had progressive disease. Median PFS was 2.1 months (95% CI 1.2-5.3). All pts experienced adverse events (AEs) and 23 experienced treatment-related AEs (TRAEs), most commonly diarrhea (n=15; 60%), nausea (n=10; 40%) and platelet count decreased (n=8; 32%). The most common grade ≥3 TRAEs were thrombocytopenia (n=4; 16%) and neutropenia (n=3; 12%). No AEs of hyperglycemia or blood glucose increased were reported. Serious AEs were experienced by 13 pts (52%). 2 pts had fatal serious AEs due to disease progression and respiratory failure. Conclusion: The combination of xentuzumab and abemaciclib showed preliminary efficacy in pts with NSCLC who had progressed on chemotherapy and an immune checkpoint inhibitor. One PR was reported. The combination had a manageable safety profile. Citation Format: Patricia LoRusso, Javier García-Corbacho, Fadi S. Braiteh, Anthony Gonçalves, Francesco Ricci, Hiroji Iwata, Marta Capelán, Marie Paule Sablin, Aleix Prat, Molly Catherine Hardebeck, Marta Puig, Dennis Chin-Lun Huang, Mingchi Hsu, Douglas Yee. An open label, multi-cohort, phase Ib study of xentuzumab and abemaciclib: Preliminary results from the advanced non-small cell lung cancer (NSCLC) cohort [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT165.

Background: We hypothesized that the abundance of PD1 mRNA in tumor samples might explain the differences in overall response rates (ORR) observed following anti-PD1 monotherapy across cancer types. Patients and methods: RNASeqv2 data from 10 078 tumor samples representing 34 different cancer types was analyzed from TCGA. Eighteen immune-related gene signatures and 547 immune-related genes, including PD1, were explored. Correlations between each gene/signature and ORRs reported in the literature following anti-PD1 monotherapy were calculated. To translate the in silico findings to the clinical setting, we analyzed the expression of PD1 mRNA using the nCounter platform in 773 formalin-fixed paraffin embedded (FFPE) tumor samples across 17 cancer types. To test the direct relationship between PD1 mRNA, PDL1 immunohistochemistry (IHC), stromal tumor-infiltrating lymphocytes (sTILs) and ORR, we evaluated an independent FFPE-based dataset of 117 patients with advanced disease treated with anti-PD1 monotherapy. Results: In pan-cancer TCGA, PD1 mRNA expression was found strongly correlated (r > 0.80) with CD8 T-cell genes and signatures and the proportion of PD1 mRNA-high tumors (80th percentile) within a given cancer type was variable (0%–84%). Strikingly, the PD1-high proportions across cancer types were found strongly correlated (r ¼ 0.91) with the ORR following antiPD1 monotherapy reported in the literature. Lower correlations were found with other immune-related genes/signatures, including PDL1. Using the same population-based cutoff (80th percentile), similar proportions of PD1-high disease in a given cancer type were identified in our in-house 773 tumor dataset as compared with TCGA. Finally, the pre-established PD1 mRNA FFPE-based cutoff was found significantly associated with anti-PD1 response in 117 patients with advanced disease (PD1-high 51.5%, PD1-intermediate 26.6% and PD1-low 15.0%; odds ratio between PD1-high and PD1-intermediate/low ¼ 8.31; P < 0.001). In this same dataset, PDL1 tumor expression by IHC or percentage of sTILs was not found associated with response. Conclusions: Our study provides a clinically applicable assay that links PD1 mRNA abundance, activated CD8 T-cells and anti-PD1 efficacy.

Purpose Pegylated arginine deiminase (ADI-PEG 20) depletes essential amino acid levels in argininosuccinate synthetase 1 (ASS1) -negative tumors by converting arginine to citrulline and ammonia. The main aim of this study was to determine the recommended dose, safety, and tolerability of ADI-PEG 20, cisplatin, and pemetrexed in patients with ASS1-deficient malignant pleural mesothelioma (MPM) or non-small-cell lung cancer (NSCLC). Patients and Methods Using a 3 + 3 + 3 dose-escalation study, nine chemotherapy-naïve patients (five MPM, four NSCLC) received weekly ADI-PEG 20 doses of 18 mg/m

2501 Background: Durvalumab (MEDI4736), a programmed cell death-ligand 1 (PD-L1) blocking antibody, is currently approved for treatment of several cancer types. As HIV-1-infected (HIV+) patients have been excluded from cancer clinical trials, there are no data on the safety of durvalumab in this population. Methods: DURVAST (NCT03094286) is a multicenter, open-label, phase 2 clinical trial evaluating the safety and feasibility of durvalumab treatment at the recommended dose of 1500 mg Q4W in HIV+ cancer patients with solid tumors. Secondary endpoints include analyses of antitumoral activity in terms of objective response rate and duration of response (DOR). An associated translational sub-study includes the assessment of antiviral activity and the interaction of chronic viral infection with anti-cancer response and drug tolerance. Results: Twenty HIV+ individuals with advanced solid tumors were enrolled (Table). All participants maintained their standard-of-care antiretroviral therapy. Basal plasma viremia was undetectable and CD4+ T-cell count was over 200/mm3. There were no durvalumab-related serious adverse events. Only 8 patients (40%) presented drug-related adverse events (all grade 1-2) including diarrhea (15%), rash (15%), nausea (15%) and asthenia (10%). Best response includes: partial response in 5 (25%) (4 NSCLC and 1 anal cancer), stable disease in 4 (20%) (3 NSCLC and 1 melanoma) and progression disease in 11 (55%) patients. At data cut-off, 8 patients (40%) remained on therapy for a median of 10.5 months (range: 6-19 m). Median DOR has not been reached (range 1m to 19 m+). Plasma viremia remained suppressed during the study suggesting no viral reactivation upon durvalumab treatment. Conclusions: DURVAST study demonstrates durvalumab safety in HIV+ cancer patients and suggests an excellent tolerance profile. Understanding how chronic viral infection could contribute to a better tolerance towards immune checkpoint inhibitors will open a new way for the development of safer anti-cancer immunotherapy strategies. Clinical trial information: NCT03094286. [Table: see text]

2513 Background: Anti-programmed cell death ligand 1 (PD-L1) immunotherapies have improved survival in many cancers, but immune-related adverse events (irAEs) have been observed, especially in combination therapy. CX-072 is an investigational Probody therapeutic directed against PD-L1, designed to be preferentially activated in the tumor microenvironment and to reduce irAEs. Methods: This is an ongoing phase 1/2a study (PROCLAIM-CX-072; NCT03013491) evaluating CX-072 in patients (pts) with metastatic or unresectable solid tumors with no further standard curative treatment options and with no prior anti-PD1, PD-L1 or anti-CTLA4 treatment. Pts were unselected for PD-L1 expression. We report preliminary results from expansion cohorts in anal squamous cell carcinoma (SCCA), cutaneous squamous cell carcinoma (cSCC), small bowel adenocarcinoma (SBA), triple-negative breast cancer with skin lesions (TNBC), or undifferentiated pleomorphic sarcoma (UPS). Pts were treated with CX-072 monotherapy 10 mg/kg intravenously every 14 days. Results: As of 30 Nov 2018, 51 pts received CX-072 10 mg/kg monotherapy: SCCA (n = 9), cSCC (n = 5), SBA (n = 9), TNBC (n = 9), and UPS (n = 19). Median age was 63 y (range, 32-80), 67% were female, and pts had a median of 3 prior regimens (range, 1-12). Median treatment duration was 1.8 mo (range, 0.3-14.7). A grade 3/4 treatment-related adverse event (AE) was observed in 1 pt (2%; gr 3 generalized rash). No grade 3/4 irAEs were observed. Two pts discontinued treatment due to AEs: nausea (pt with SCCA) and sepsis (pt with SBA), neither treatment-related. Partial responses (confirmed and unconfirmed) were observed in cSCC (n = 1), TNBC (n = 2), and UPS (n = 1) (Table). Conclusions: CX-072 10 mg/kg monotherapy demonstrated anticancer activity in heavily pretreated pts with advanced solid tumors, including responses in cSCC, TNBC with skin lesions, and UPS, with a safety profile that compares favorably to historical controls. Clinical trial information: NCT03013491. [Table: see text]

TPS1101 Background: MEN1611 is a potent, selective class I inhibitor of PI3K, a key enzyme in the transduction of various extracellular growth factor signals essential for cell survival and apoptosis. The discovery in human cancers of frequent PIK3CA mutations, that have been linked to a worse outcome in advanced HER2-positive breast cancer, makes PI3K an attractive therapeutic target. Preclinical and clinical evidences support the development of MEN1611 in combination with other agents in the context of solid tumors. Methods: B-PRECISE-01 is an open-label, multicenter, phase Ib dose escalation study in patients with PIK3CA mutant tumors, HER2-positive advanced or metastatic breast cancer which has progressed after at least 2 lines of anti-HER2 based therapy. PIK3CA mutations are assessed centrally by real-time PCR assay in DNA derived from archived tumor samples. MEN1611 will be administered orally BID for continuous 28-day cycles until disease progression, in combination with weekly IV infusions of trastuzumab. In addition, HR-positive postmenopausal patients will also be treated with fulvestrant. After the completion of the dose escalation phase (Step 1), the study will continue in an expansion cohort (Step 2) testing the Recommended Phase 2 dose (RP2D) in a total of 15 patients in each of the treatment groups. The primary study objective is to assess combination safety and select RP2D. Secondary objectives include assessment of pharmacokinetics and pharmacodynamics, preliminary clinical activity of MEN1611 in combination with trastuzumab +/- fulvestrant, and correlation with PIK3CA mutations and other relevant cancer genes mutational status. Adverse events will be graded according to NCI CTCAE v4.03. Responses will be evaluated according to RECIST v1.1. Study variables will be presented by dose-cohort and overall using appropriate descriptive statistics. The enrollment began in July 2018 at European sites and US sites will shortly participate; up to date the first dose cohort level has been achieved. Clinical trial information: NCT03767335.