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Our goal was to review the history of the adoption of focal therapy for breast and prostate cancer and review common barriers to implementation.A narrative review of the literature was performed of English-language MEDLINE indexed articles of breast-conservation therapy and prostate cancer focal therapy.The introduction of focal therapy in breast cancer began with pioneering case series, and multiple randomized trials were performed prior to widespread adoption. Focal therapy for prostate cancer has just started the process of clinical trials with a single published randomized controlled trial. Commonly cited barriers to the adoption of prostate focal therapy include historical views of Halstedian tumor biology, tumor multifocality, over-detection, limitations in prostate imaging, and trial design end points.The adoption of breast-conserving therapy evolved over decades and used data from multiple large, randomized, clinical trials. Barriers to the adoption of prostate cancer local therapy are similar to those faced by breast cancer clinical trials. Completion of well-designed trials in prostate cancer focal therapy is essential for its evidence-based adoption.

We performed a 318-participant validation study of an individualized risk assessment tool in women identified as having high- or highest-risk of breast cancer in the personalized arm of the Women Informed to Screen Depending on Measures of risk (WISDOM) trial. Per protocol, these women were educated about their risk and risk reducing options using the Breast Health Decisions (BHD) tool, which uses patient-friendly visuals and 8th grade reading level language to convey risk and prevention options. Prior to exposure to the educational tool, 4.7% of women were already taking endocrine risk reduction, 38.7% were reducing alcohol intake, and 62.6% were exercising. Three months after initial use of BHD, 8.4% of women who considered endocrine risk reduction, 33% of women who considered alcohol reduction, and 46% of women who considered exercise pursued the risk-reducing activities. Unlike lifestyle interventions which are under the control of the patient, additional barriers at the level of the healthcare provider may be impeding the targeted use of endocrine risk reduction medications in women with elevated breast cancer risk.

Introduction: Ductal carcinoma in situ (DCIS) of the breast is a premalignant lesion representing a spectrum of biology from indolent to aggressive. A minority of women present with clinically high-risk features associated with poor outcome. Yet even in patients with biologically aggressive DCIS, the risk of breast cancer mortality is only 3.3% compared to 30-40% in patients with biologically aggressive invasive cancer of the same size.1 We hypothesize that the tumor immune microenvironment could play a proactive role in preventing invasion in high grade clinically high-risk DCIS and that HER2 status, including specific HER2 isoform expression and post-translational modification of HER2, could impact progression. Methods: DCIS: Elaboration of Factors from Enlarged lesions that Nevertheless remain Stage 0 Entities (DEFENSE) is a study of high-risk DCIS, defined as having at least two of the following characteristics: large (>5cm), high grade, hormone receptor-negative status and/or HER2+ status. Slides obtained from FFPE tissue blocks were stained with fluorescence-based multiplex immunohistochemistry (mIHC) panels and imaged to characterize immune infiltrate within the ducts and the stromal compartments. mIHC was also used to detect extracellular and intracellular domains of HER2 with imaging analysis performed to identify HER2 isoforms of HER2+ specimens. Isoforms were characterized as 1) full-length/extracellular domain (ECD) intact, 2) pure/complete loss of ECD (p95 isoform), 3) subclonal populations of both full-length ECD and p95 and 4) gradient/representing partial loss of ECD per cell (reflecting post-translational cleavage). Clinical characteristics were correlated with molecular profile, tumor immune infiltrates, and HER2 isoform. Finally, expression profiling with a 44k array was conducted by Agendia, and MammaPrint and BluePrint results were generated. Results: Of 92 total patients, median age is 46 years. The average DCIS lesion size is 8.2cm, and 33% are hormone receptor negative (HR-). Based upon initial analysis, mIHC demonstrates significant heterogeneity in immune infiltrate populations of pathologically identical DCIS specimens and within regions of the same specimen. High-grade HR- disease has highly reactive stroma, characterized by dense CD3+, CD34+, and CD68+ infiltrate within the stromal compartment. HER2 testing of the first 51 cases demonstrates a high rate of positivity of 67% (34/51). Of those tested for HER2 isoform expression (n=21), none had homogeneous intact full-length HER2. Six (29%) demonstrate the pure p95 isoform, 3 (14%) demonstrate the subclonal isoform, and 12 (57%) demonstrate a gradient HER2 isoform phenotype. Preliminary data from expression profiling shows that the HER2+ cases are also HER2 intrinsic sub-type by BluePrint. Across all of the high-risk DCIS cases, all were scored as MammaPrint high risk, either Luminal B or HER2-type, with only 1 basal and no Luminal A. Additional analyses are ongoing, including completion of testing for the whole data set as well whole exome DNA sequencing and SMART-3SEQ RNA sequencing. Conclusions: Clinically high-risk and pathologically homogenous DCIS lesions demonstrate significant immune infiltrate heterogeneity. Nearly 70% of these large clinically high-risk DCIS lesions are HER2+ with HER2 isoforms most commonly representing either partial or complete loss of the HER2 ECD. This is significantly higher than what is reported for invasive HER2+ breast cancer. A comparison to size and molecularly matched invasive cancers, including from the I-SPY 2 trial, is underway in an effort to elucidate how molecularly aggressive lesions remain in situ despite their large size. References:1 Narod SA et al (2015). Breast Cancer Mortality After a Diagnosis of Ductal Carcinoma in Situ. JAMAOncol. 1(7): 888-96. Citation Format: Alexa Glencer, Alexander Borowsky, Hidetoshi Mori, Michael Campbell, Olivier Harismendy, Janet Stein, Prachi Ghule, Mark Evans, Robert West, Gillian Hirst, Nicole Schindler, Phoebe Miller, Kyra Lee, Donald Weaver, Laura Esserman. The tumor immune microenvironment and HER2 landscape of high-risk ductal carcinoma in situ: The DEFENSE study [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 P1-05-01.

Introduction: Advances in technology and internet capability have provided an opportunity for efficient collection of Patient Reported Outcomes (PRO) during medical treatment. Here we describe the development and implementation of a system for monitoring patient reported adverse events (AEs) and quality of life (QoL) using electronic PRO (ePRO) instruments for patients enrolled on the Investigation of Serial studies to Predict Your Therapeutic Response with Imaging And moLecular analysis (I-SPY 2 TRIAL), a phase II adaptive platform clinical trial for locally advanced breast cancer. Methods: We designed an ePRO system to increase the accuracy of patient-reported QoL and AE data collection with the intent to act on symptoms in real time. Using the OpenClinica electronic data capture system, we developed rules-based logic to build automated ePRO surveys, customized to the I-SPY 2 treatment schedule. Weekly surveys contained a maximum of 126 validated, branching logic questions from the Patient Reported Outcomes Measurement Information System (PROMIS®) Health Measures and the National Cancer Institute’s Patient Reported Outcomes - Common Terminology Criteria for Adverse Events (PRO-CTCAE™) instruments. We piloted ePROs at the University of California, San Francisco (UCSF) to evaluate compatibility with a variety of I-SPY 2 patient scenarios (e.g., dose delays). We then staggered rollout of the ePRO system to 22 I-SPY 2 sites to ensure technological feasibility. In order to improve accuracy of data collection, we utilized real-time tracking and developed a Clinical Research Coordinator (CRC) training manual, which integrated workflow diagrams with technical solutions. CRCs were trained using remote video sessions. Results: The UCSF ePRO pilot began in September of 2020. Over 9-months, we accrued 43 I-SPY 2 patients (average age of 43.8 years), whose interactions with the ePRO system informed design improvements. Of the patients who received a baseline ePRO survey, the completion rate was 75.9% (average age of 44.2 years). This represents an increase from the 15-20% baseline completion rate for the 360 UCSF I-SPY 2 patients who received paper-based PRO surveys between May 2012 - January 2019. As of June 2021, the ePRO system was operational at all 22 I-SPY 2 sites. The UCSF pilot revealed that engagement with patients at critical timepoints improved survey completion. CRCs facilitated patient participation by sending instructional emails and communicating with patients weekly. We tracked data completeness using a Patient Tracking report, which displayed each patient’s survey completion history. This real-time tool enabled CRCs to identify patients who had not completed ePRO surveys prior to their visit, so they could be provided a tablet computer to complete the survey in the clinic. After introducing tablets into the workflow at UCSF, patient completion of the baseline survey increased from 75.9% to 80%. Conclusion: The transition from paper to electronic QOL and AE data collection improves the ability of patients to complete PRO surveys, but the process must also be optimized and integrated into clinical workflow and trial conduct. In the future, we will present additional results highlighting the feasibility of multilingual ePRO integration into I-SPY 2. ePRO also provides a new opportunity for data analysis, as well as the potential to reduce high grade toxicity through early intervention. It will allow us to assess QoL and AE data by drug regimen, site, provider, and study treatment. The creation of clinician-facing reports also enables access to patient responses in real-time. By implementing ePRO within I-SPY 2, we not only increase efficiency and accuracy of patient-reported data collection, but also improve quality of care and patient safety. Citation Format: Anna Northrop, Anika Christofferson, Michelle Melisko, Laura Sit, Ebunoluwa Olunuga, Ananya Mittal, Adi Goldman, Thelma Brown, Diane Heditsian, Bev Parker, Susie Brain, Carol Simmons, Alessandra Taboada, Kathryn J Ruddy, Tina Hieken, Mara Piltin, Kiri Cook, Carolina Salvador, Candace Mainor, Anosheh Afghahi, Sarah Tevis, Anne Blaes, Irene Kang, Susan Melin, Laura Esserman, Adam Asare, Dawn L Hershman, Amrita Basu. Improving patient-reported outcome data capture for clinical research: ePRO in ISPY 2, a phase 2 breast cancer study [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 P4-12-02.

Background: The CK12 expression signature consists of genes CCL2, CCL3, CCL4, CCL5, CCL8, CCL18, CCL19, CCL21, CXCL9, CXCL10, CXCL11, CXCL13 and was previously shown to associate with the presence of T and B cell rich tertiary lymphoid structures in melanoma and other cancers, and with better patient survival independent of tumor staging and treatment. I-SPY 2 is a biomarker-rich, phase II neoadjuvant platform trial for high risk early stage breast cancer. Here we leverage the I-SPY 2 biomarker program to test the hypothesis that this signature associates with sensitivity to neoadjuvant immunotherapies and potentially other classes cancer therapeutics in breast cancer. Methods: Data from 1130 patients across 12 arms of I-SPY2 (control (ctr): 210; veliparib/carboplatin (VC): 71; neratinib (N): 114; MK2206: 93; ganitumab: 106; ganetespib: 93; AMG386: 134; TDM1/pertuzumab(P): 52; H/P: 44; pembrolizumab (pembro): 69; durvalumab/olaparib (durva/olap): 71; pembro/SD101: 72) were available for analysis. Pre-treatment FF (n=987) or FFPE (n=143) biopsies were assayed using Agilent gene expression arrays. Signature scores were calculated as the average expression level across the 12 genes, after z-score normalization. We used logistic modeling to assess association with pCR in each arm in a model adjusting for HR and HER2 (likelihood ratio test, p Citation Format: Hatem Soliman, Denise Wolf, Jo Chien, Christina Yau, Michael Campbell, Mark Magbanua, Ruixiao Lu, Nicholas O'Grady, Lamorna Brown-Swigart, Gillian Hirst, Beverly Parker, Laura Sit, Smita Asare, Doug Yee, Angie DeMichele, Rita Nanda, Lajos Pusztai, Don Berry, Laura Esserman, Laura Van't Veer. Chemokine12 (CK12) tertiary lymphoid gene expression signature as a predictor of response in 3 immunotherapy arms of the neoadjuvant ISPY 2 TRIAL - pembrolizumab with and without SD101, and durvalumab combined with olaparib - and in 9 other arms of the trial including platinum-based and dual-anti-HER2 therapies [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 PD10-07.

PDF file - 103K, Validation of the reproducibility of the RPMA for HER2 and pHER2 analysis from FFPE-tissues

Purpose:We examined the prognostic impact of circulating tumor cells (CTCs) and disseminated tumor cells (DTCs) detected at the time of surgery in 742 untreated patients with early breast cancer.Experimental Design:DTCs in bone marrow were enumerated using the EPCAM-based immunomagnetic enrichment and flow cytometry (IE/FC) assay. CTCs in blood were enumerated either by IE/FC or CellSearch. Median follow-up was 7.1 years for distant recurrence-free survival (DRFS) and 9.1 years for breast cancer–specific survival (BCSS) and overall survival (OS). Cox regressions were used to estimate hazard ratios for DRFS, BCSS, and OS in all patients, as well as in hormone receptor–positive (HR-positive, 87%) and HR-negative (13%) subsets.Results:In multivariate models, CTC positivity by IE/FC was significantly associated with reduced BCSS in both all (n = 288; P = 0.0138) and HR-positive patients (n = 249; P = 0.0454). CTC positivity by CellSearch was significantly associated with reduced DRFS in both all (n = 380; P = 0.0067) and HR-positive patients (n = 328; P = 0.0002). DTC status, by itself, was not prognostic; however, when combined with CTC status by IE/FC (n = 273), double positivity (CTC+/DTC+, 8%) was significantly associated with reduced DRFS (P = 0.0270), BCSS (P = 0.0205), and OS (P = 0.0168). In HR-positive patients, double positivity (9% of 235) was significantly associated with reduced DRFS (P = 0.0285), BCSS (P = 0.0357), and OS (P = 0.0092).Conclusions:Detection of CTCs in patients with HR-positive early breast cancer was an independent prognostic factor for DRFS (using CellSearch) and BCSS (using IE/FC). Simultaneous detection of DTCs provided additional prognostic power for outcome, including OS.

PDF file - 54K, Antibodies used for Array and Western Blot Immunostaining

Purpose: Targeting of the HER2 protein in human breast cancer represents a major advance in oncology but relies on measurements of total HER2 protein and not HER2 signaling network activation. We used reverse-phase protein microarrays (RPMA) to measure total and phosphorylated HER2 in the context of HER family signaling to understand correlations between phosphorylated and total levels of HER2 and downstream signaling activity.Experimental Design: Three independent study sets, comprising a total of 415 individual patient samples from flash-frozen core biopsy samples and formalin-fixed and paraffin-embedded (FFPE) surgical and core samples, were analyzed via RPMA. The phosphorylation and total levels of the HER receptor family proteins and downstream signaling molecules were measured in laser capture microdissected (LCM) enriched tumor epithelium from 127 frozen pretreatment core biopsy samples and whole-tissue lysates from 288 FFPE samples and these results were compared with FISH and immunohistochemistry (IHC).Results: RPMA measurements of total HER2 were highly concordant (>90% all sets) with FISH and/or IHC data, as was phosphorylation of HER2 in the FISH/IHC+ population. Phosphorylation analysis of HER family signaling identified HER2 activation in some FISH/IHC− tumors and, identical to that seen with FISH/IHC+ tumors, the HER2 activation was concordant with EGF receptor (EGFR) and HER3 phosphorylation and downstream signaling endpoint activation.Conclusions: Molecular profiling of HER2 signaling of a large cohort of human breast cancer specimens using a quantitative and sensitive functional pathway activation mapping technique reveals IHC−/FISH−/pHER2+ tumors with HER2 pathway activation independent of total HER2 levels and functional signaling through HER3 and EGFR. Clin Cancer Res; 18(23); 6426–35. ©2012 AACR.

Supplementary Figures and Tables except Table S7

Crucial transitions in cancer-including tumor initiation, local expansion, metastasis, and therapeutic resistance-involve complex interactions between cells within the dynamic tumor ecosystem. Transformative single-cell genomics technologies and spatial multiplex in situ methods now provide an opportunity to interrogate this complexity at unprecedented resolution. The Human Tumor Atlas Network (HTAN), part of the National Cancer Institute (NCI) Cancer Moonshot Initiative, will establish a clinical, experimental, computational, and organizational framework to generate informative and accessible three-dimensional atlases of cancer transitions for a diverse set of tumor types. This effort complements both ongoing efforts to map healthy organs and previous large-scale cancer genomics approaches focused on bulk sequencing at a single point in time. Generating single-cell, multiparametric, longitudinal atlases and integrating them with clinical outcomes should help identify novel predictive biomarkers and features as well as therapeutically relevant cell types, cell states, and cellular interactions across transitions. The resulting tumor atlases should have a profound impact on our understanding of cancer biology and have the potential to improve cancer detection, prevention, and therapeutic discovery for better precision-medicine treatments of cancer patients and those at risk for cancer.

Background: The SET2,3 index combines an accurate measure of transcription related to both estrogen and progesterone receptors (SETER/PR index) with a baseline prognostic index (BPI) derived from c-T Stage, c-N status and molecular subtype by RNA4 (ESR1, PGR, ERBB2, and AURKA). SET2,3 index was translated from a microarray-based signature to a customized hybridization assay that yields highly reproducible results from routine pathology tissue blocks. Methods: The SET2,3 index was calculated from microarray data prepared from baseline biopsies of HR+/HER2- cancers prior to neoadjuvant taxane-anthracycline chemotherapy followed by adjuvant endocrine therapy in: 1) a test set of 307 samples from the MDACC cohort with 8 years median follow-up (Affymetrix U133A microarrays, Symmans et al JAMA 2011), and 2) an independent blinded validation set of 268 high-risk Mammaprint (MP) samples from the I-SPY2 clinical trial with 3.8 years median follow-up (Agilent 44K microarrays, Agendia). The cut-point for high versus low SET2,3 was defined in the MDACC cohort and then tested in the I-SPY2 cohort. Association between the SET2,3 index and distant relapse-free survival (DRFS) was evaluated in each cohort using multivariate Cox regression models. One model adjusted for residual cancer burden (RCB) after neoadjuvant chemotherapy and its interaction with the SET2,3 index, also including treatment arm (experimental vs. control) in the I-SPY 2 trial. Another model adjusted for other prognostic gene expression signatures (GES) for recurrence score (RS), MP, or endopredict (EP) in the MDACC cohort, and actual MP in the I-SPY2 trial. A third model tested the ability of prognostic GES to substitute for RNA4 subtype (part of BPI) or SETER/PR index as components of the SET2,3 index. Results: Predicted sensitivity to endocrine therapy (SET2,3) and response to neoadjuvant chemotherapy (RCB) were independently prognostic, with nonsignificant (NS) interaction term, in multivariate analyses of the MDACC study: SET2,3 HR 0.26 (p=0.016); RCB HR 2.04 (p Conclusions: SET2,3 index of endocrine transcriptional activity in a pre-treatment core biopsy added independent significant prognostic information to any baseline prognostic score and response to neoadjuvant chemotherapy. Approximately 40% of clinical or genomic (MP) high-risk HR+/HER2- cancers had high SET2,3 index, and their response to neoadjuvant chemotherapy (RCB class) was not prognostic. This suggests that SET2,3 index might be used to select appropriate candidates for endocrine-based neoadjuvant treatments in clinical trials. Citation Format: Lili Du, Christina Yau, Lamorna Brown-Swigart, Rebekah Gould, Gillian L Hirst, I-SPY2 Consortium, Marieke van der Noordaa, Isabelle Bedrosian, Rachel M Layman, Vicente Valero, Laura van't Veer, Laura Esserman, W. Fraser Symmans. Prognostic contribution of predicted sensitivity to endocrine therapy (SET) prior to neoadjuvant chemotherapy for stage II-III hormone receptor-positive and HER2-negative (HR+/HER2-) breast cancer [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 P2-11-04.

Background: Aggressive breast cancers have increased proliferation or metastatic potential and portend a poor prognosis. The ability to identify women at elevated risk of aggressive cancers could have major implications for screening and prevention, yet there are no available tools for predicting aggressive cancer risk. We sought to construct a polygenic risk score (PRS) for aggressive breast cancers by leveraging the associations of single nucleotide polymorphisms (SNPs) with tumor gene expression. We used as our measure of aggressiveness the risk of recurrence score weighted on proliferation (ROR-P), a validated tumor prognostic signature. We hypothesized that known breast cancer susceptibility SNPs would have differential associations with ROR-P, which could then be used to construct a PRS for ROR-P. Methods: We developed our PRS in a case-only analysis of 3 studies containing SNP genotypes and tumor gene expression: The Cancer Genome Atlas, METABRIC, and the I-SPY 2 TRIAL (total n=2,363). We used linear regression models to evaluate individual SNP associations with ROR-P, adjusted for genetic ancestry and study. We then constructed PRS using varying p-value thresholds and used cross-validation to identify the PRS with highest model r2. To assess whether the ROR-P PRS was associated with poor prognosis, we performed survival analysis in two longitudinal cohorts of breast cancer patients: the UK Biobank (women with incident invasive cancers only) and the Pathways Study. These studies included 10,196 total cases with 785 deaths. We built Cox proportional hazards models to evaluate the association between the ROR-P PRS (adjusted for genetic ancestry) and breast cancer-specific survival (BCSS) in both studies. We then performed meta-analysis of the Cox model results. We also constructed joint models containing the ROR-P PRS and a PRS representing the case-case risk of ER-negative vs. ER-positive cancer, PRSER-/ER+. Results: We tested the associations between 226 breast cancer susceptibility SNPs and ROR-P. The best-performing PRS contained 76 SNPs and had a cross-validated r2 of 0.051. In the UK Biobank and Pathways Study, higher ROR-P PRS was associated with worse BCSS, with nearly identical effects observed in each study, HR per standard deviation of 1.13 (95% CI 1.05-1.21, p=9.0x10-4) in meta-analysis. The ROR-P PRS’s effect was minimally attenuated when adjusted for PRSER-/ER+, suggesting that the ROR-P PRS was providing additional prognostic information beyond ER status. Conclusions: We used breast cancer susceptibility SNPs to construct a PRS for ROR-P, a prognostic signature recapitulating aggressiveness, and found the ROR-P PRS to be associated with worse BCSS. Our findings represent an improvement on current PRS for overall breast cancer risk, which preferentially predict cancers with favorable prognosis. Given that aggressive cancers are more likely to present as advanced cancers even among women undergoing routine screening, our findings could potentially identify women who may benefit from more intensive screening. Citation Format: Yiwey Shieh, Jacquelyn Roger, Christina Yau, Denise Wolf, Gillian Hirst, Lamorna Swigart, Scott Huntsman, Donglei Hu, Jovia Nierenberg, Pooja Middha, Rachel Heise, Linda Kachuri, Qianqian Zhu, Song Yao, Christine Ambrosone, Marilyn Kwan, Bette Caan, John Witte, Lawrence Kushi, Laura van ’T. Veer, Laura Esserman, Elad Ziv. Development and testing of a polygenic risk score for breast cancer. Aggressiveness. [abstract]. In: Proceedings of the AACR Special Conference: Precision Prevention, Early Detection, and Interception of Cancer; 2022 Nov 17-19; Austin, TX. Philadelphia (PA): AACR; Can Prev Res 2023;16(1 Suppl): Abstract nr PR008.

Background: Ductal carcinoma in situ (DCIS) represents almost a quarter of newly diagnosed breast cancers in the US. It is currently treated like a stage 1 cancer, with surgical excision, radiation, and endocrine therapy (ET). Not all cases will progress to invasive cancer and thus we may be overtreating some lesions. Using a cohort of women who participated in an Active Surveillance (AS) with neoadjuvant ET and serial MR imaging, we aimed to identify features on MRI that could stratify DCIS lesions with low- and high-risk of progressing to invasive cancer. Materials/Methods: This was an IRB-approved retrospective study of women with DCIS who chose AS for treatment and were enrolled in MR imaging studies between 2002 and 2020. All women in this study had at least 2 breast MRI scans, which consisted of normal sequences with two post-contrast timepoints. Two radiologists, who were blinded to outcomes, analyzed MRI sequences for each patient at each timepoint for features that may be indicative of risk. Baseline imaging features collected were utilized in an RPART recursive partitioning algorithm that created a classification tree based on a DCIS lesions likelihood to progress to invasive cancer. Our final cohort consisted of 63 cases of DCIS (62 women, 1 with bilateral disease) with a mean age of 58.3 years (range of 29.8-78.8 years). All 62 patients (63 cases, 100%, 63/63) agreed to take hormone therapy for their DCIS. Results: The RPART algorithm showed two baseline features that were important in predicting risk: 1) the presence of a lesion that is distinct from the surrounding tissue and 2) background parenchymal enhancement (BPE). It separated our cohort into three sub-groups based on risk of progression: A (n=32) with the lowest-risk, B (n=17) with the second lowest-risk, and C (n=14) with the highest-risk. In A and B, 6 cases of DCIS progressed to invasive cancer (12.2%, 6/49). These groups had an enrichment of mild, moderate, and marked BPE. Group A (12.5%, 4/32 progressed to IDC) did not have any lesions that were distinct above BPE. All cases in B (11.8%, 2/17 progressed to IDC) had lesions that were distinct above BPE initially but reduced in response to endocrine therapy. In C, 10 cases of DCIS progressed to invasive cancer (71.4%, 10/14). In this group, the combination of minimal BPE and a distinct lesion above BPE was enriched (78.6%, 11/14). Conclusion: Our results suggest that imaging features, such as BPE, lesion distinctness and change in BPE and lesion provide information about risk for invasive cancer. MRI features provide insight as to whether risk is diffuse or focal, and which women can safely undergo AS with hormone treatment and avoid surgery, and which women are at higher-risk and have focal lesions better treated with surgical excision. We plan to validate the use of these features to triage patients in an upcoming prospective multisite trial to stratify DCIS patients for active surveillance vs. surgical resection. Citation Format: Cristian K. Maldonado Rodas, Heather Greenwood, Rita Freimanis, Alexander D. Borowsky, Gillian Hirst, Nola Hylton, Laura Esserman, Amrita Basu. MRI features can identify DCIS patients who can be managed with endocrine therapy alone [abstract]. In: Proceedings of the AACR Special Conference on Rethinking DCIS: An Opportunity for Prevention?; 2022 Sep 8-11; Philadelphia, PA. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_1): Abstract nr B015.

Background: Ductal carcinoma in situ (DCIS) is a risk factor for the development of invasive ductal carcinoma. Previous work has shown that an increased presence of T cells corresponds to high-risk DCIS features: age 5 cm, high-grade, palpable mass, hormone receptor negativity, and HER2 positivity. The presence of T cells colocalized with tumor is emerging as a predictor of response to checkpoint inhibition in invasive cancer. We previously have demonstrated that intratumoral injections of a checkpoint inhibitor (pembrolizumab) in DCIS resulted in an increased number of T cells, but without tumor cell killing. We hypothesized that the addition of an agent that could potentiate both innate and adaptive immune responses might increase the efficacy of checkpoint inhibition. Methods/Materials: We administered intralesional injections of immunotherapy (4-8 mg pembrolizumab + 2-4mg mRNA 2752) to patients with “high-risk” DCIS in an attempt to modulate the immune system and protect from disease progression and recurrence. Two patients have been enrolled and completed therapy and 4 more are being treated. Immune infiltrates were characterized by multiplex immunofluorescence (mIF) staining of pre- and post-treatment tissue samples using two 6-plex panels. Staining was performed on a Leica Bond autostainer and images were acquired on a Vectra Polaris imaging system. Image analysis was performed utilizing inForm and QuPath software packages, as well as R scripts. Results: The first patient treated, a 41-year-old woman with ER+/PR+, HER2- disease, with low T cells in her pre-treatment biopsy, received one dose of pembrolizumab (8mg) with mRNA 2752 (4mg). While she experienced fatigue, sustained fever, and muscle aches for 3-5 days, draining node enlargement and redness and swelling at the breast a week after treatment, there was no change on her post-treatment MRI, and no significant change in the number of T cells in her post-treatment tissue. The second patient, a 74-year-old woman with ER-/PR-, HER2+ disease had high numbers of T cells in the pre-treatment biopsy. She received one injection of pembrolizumab (4mg) with mRNA 2752 (2mg), followed 3 weeks later by an injection of pembrolizumab (4mg) alone. She declined the second dose of mRNA 2752 due to side effects from the first injection. Her post-treatment MRI showed some reduction in tumor volume and her post-treatment biopsy showed no evidence of DCIS, as well as an increase in T cells. Conclusions: The presence of T cells prior to therapy is likely to be important for eliciting a strong anti-tumor response. The addition of an agent that enhances both innate and adaptive immune responses may increase the efficacy of immune checkpoint blockade. Four additional patients will have completed their therapy by the end of August and we await results. It will be important to understand if pre-existing T cells within the DCIS lesion are a predictor for response to therapy as we continue to screen and enroll patients. Citation Format: Nicole F. Schindler, Alexa Glencer, Phoebe Miller, Christopher Schwartz, Gillian Hirst, Alexander Borowsky, Michael Campbell, Laura Esserman. Intralesional injections with checkpoint inhibitors and cytokines can modify DCIS lesions with infiltrating T cells [abstract]. In: Proceedings of the AACR Special Conference on Rethinking DCIS: An Opportunity for Prevention?; 2022 Sep 8-11; Philadelphia, PA. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_1): Abstract nr B005.

Purpose: The immune microenvironment in ductal carcinoma in situ (DCIS) and its significance are not well established. In this study, we characterized the immune microenvironment of DCIS to determine if immune cell densities, or their spatial relationships with tumor cells, are predictive of recurrence with invasive breast cancer. Methods: One hundred thirty-two cases of DCIS were included in this study. Seventy (53%) cases were high grade, 72 (54%) were HER2+, and 91 (69%) were HR+. Twenty cases recurred with invasive breast cancer. Immune infiltrates were characterized by multiplex immunofluorescence staining of FFPE sections using two 6-plex panels. Panel IP1.2 included markers for CD3, CD20, Foxp3, pan-cytokeratins, Ki67, and HLADR. Panel IP2.2 included markers for CD3, CD8, CD68, pan-cytokeratins, PD-1, and PD-L1. Staining was performed on a Leica Bond autostainer and images were acquired on a Vectra Polaris imaging system. Image analysis was performed utilizing inForm and QuPath software packages, as well as R scripts. Counts for each cell population were determined and spatial point pattern analyses were performed to quantitate the spatial relationships between tumor cells and various immune cell types. Results: High infiltrates of T cells, CD8+ T cells (Tc), Foxp3+ T cells, and B cells were associated with high grade, hormone receptor (HR) negativity, HER2 positivity, and the presence of comedonecrosis. PD-1+ T cells and PD-1+ Tc were associated with high grade, HR negativity, and HER2 positivity. PD-L1+ immune cells, but not PD-L1+ tumor cells, were also associated with high grade, HR negativity, and HER2 positivity. None of the cell populations were associated with invasive recurrence. However, the spatial proximity of tumor cells with T cells, in particular Tc, was significantly associated with a subsequent invasive event. Patients whose DCIS had a high tumor-to-Tc proximity score (indicating close proximity of tumor and Tc) were less likely to have an invasive recurrence. Conclusion: These findings suggest that the tumor immune microenvironment is an important factor in identifying DCIS cases at risk for invasive recurrence and that manipulating the immune microenvironment may be an efficacious strategy to alter or prevent disease progression. Citation Format: Michael J. Campbell, Nicole Schindler, Alexa Glencer, Jennifer Bolen, Hidetoshi Mori, Tristan Loveday, Harriet Rothschild, Gillian Hirst, Scott Vandenberg, Alexander Borowsky, Laura Esserman. Spatial proximity between CD8+ T cells and tumor cells correlates with invasive recurrence in DCIS [abstract]. In: Proceedings of the AACR Special Conference on Rethinking DCIS: An Opportunity for Prevention?; 2022 Sep 8-11; Philadelphia, PA. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_1): Abstract nr PR001.

Background/Aim: Testing for human epidermal growth factor receptor 2 (HER2) positivity in women diagnosed with ductal carcinoma in situ (DCIS) is not performed routinely, although the frequency of HER2+ DCIS is at least 30%. HER2+ DCIS lesions may be at higher risk of progression to invasive carcinoma, and specific isoforms of HER2 may lead to different malignant potential. Loss of the HER2 extracellular domain engineered in mouse models demonstrates rapid progression to invasive behavior. Evaluating isoforms of HER2 may aid in classifying DCIS lesions as higher or lower risk, and may provide insight for novel treatment and prevention approaches. Methods: A cohort of high risk DCIS cases were assembled, enriched for the presence of high risk features, including large size (>5 cm) and palpable. Immunohistochemistry (IHC) and FISH were used to identify cases that were HER2 positive. MultiplexIHC was used to detect extracellular and intracellular domains of HER2, with imaging analysis performed to identify HER2 isoforms of HER2+ specimens. Isoforms were characterized as 1) full-length/extracellular domain (ECD) intact, 2) pure/complete loss of ECD (p95 isoform), 3) subclonal populations of both full-length ECD and p95 and 4) gradient/representing partial loss of ECD per cell (reflecting post-translational cleavage). Results: Out of 51 cases, 34 (67%) cases were HER2+. In multiplexIHC analysis for HER2, 51% displayed gradient (partial) or focal (subclonal) loss of the extracellular domain. 33% displayed pure p95 isoform (complete loss of ECD). Only 16% of the cohort displayed full-length HER2 extracellular domain. Conclusions: HER2 expression is much more common in large in situ lesions than in invasive lesions. This suggests that HER2 positivity may play a role in protecting against invasion. Investigation of HER2 Isoform testing using multiplex staining reveals heterogeneity with partial or complete loss of the HER2 extracellular domain being most common. Loss of the extracellular domain of human epidermal growth factor receptor 2 (HER2) p95 isoform is predominant among patients diagnosed with HER2 positive ductal carcinoma in situ (DCIS). Citation Format: Nicole F. Schindler, Alexa Glencer, Hidetoshi Mori, Gillian Hirst, Cristian Maldonado Rodas, Michael Campbell, Laura Esserman, Alexander Borowsky. Loss of the extracellular domain of human epidermal growth factor receptor 2 (HER2) p95 isoform is common in large DCIS lesions [abstract]. In: Proceedings of the AACR Special Conference on Rethinking DCIS: An Opportunity for Prevention?; 2022 Sep 8-11; Philadelphia, PA. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_1): Abstract nr B013.

Background Digital breast tomosynthesis (DBT), also called 3D mammography, was first approved by the Federal Drug Administration in 2011. The goal of 3D mammography is to improve accuracy compared to 2D digital mammography (DM), by increasing sensitivity and decreasing recall rates. To capture the broad utilization of DBT in populations receiving both screening and diagnostic imaging, this analysis investigates DBT usage over time in a longitudinal sample from 2016 through 2020 for adult women ranging from 18-74 years of age. Methods Retrospective analyses were conducted using de-identified administrative claims data from a large national U.S. health insurer. The study cohort consisted of women who were continuously enrolled in a commercial or Medicare Advantage plan from 1/2016 to 12/2020 and aged 18 to 74 years old as of 2016. All procedures were identified based on Current Procedural Terminology (CPT) and Healthcare Common Procedure Coding System (HCPCS) codes. For each study year, receipt of breast cancer screening with DM (S-DM) or including DBT (S-DBT) were captured. Receipt of DM and DBT not specified for screening based on CPT code descriptions were categorized as diagnostic, D-DM and D-DBT respectively. Women that received both DBT and DM in the same year were included in the DBT group. In addition, women who received MRI and ultrasound were also captured. Rates of each procedure by study year, insurance type, and age categories that align with recommended screening guidelines ( Table. Rates of adult women who received digital breast tomosynthesis, digital mammography, MRI and ultrasound by age group and year from 2016-2020.Calendar YearAge Group categoryTotal women with ≥1 Screening Mammography, N% with S-DBT% with S-DMTotal women with ≥1 Diagnostic Mammography Procedure, N% with D-DBT% with D-DMWomen with at least ≥1 MRI procedureWomen with ≥1 Ultrasound procedure2016Total100175523%77%20237129%71%20786227790 Citation Format: Stacey DaCosta Byfield, Kenneth Wimmer, Beatrice Amara Adajar, Peter Onglao, Annika Fredrickson, Maria Eloisa Ventura, James Staib, Kierstin Catlett, Rashna Soonavala, Mi-Ok Kim, Allison Fiscalini, Laura Esserman. Real world evidence demonstrates replacement of 2D mammography with 3D mammography among insured women [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 P3-04-02.

Background Patients with breast cancer frequently experience escalation of anxiety after completing curative treatment. Objective This study evaluated the acceptability and psychological impact of a 1-day workshop to emphasize behavioral strategies involving intention and self-efficacy. Methods Breast cancer survivors who attended a 1-day Pathways for Survivors workshop provided feedback and completed electronic quality of life (QOL) questionnaires at baseline, 1 and 6 weeks, and 6 months after the workshop. Attendees’ baseline QOL scores were compared to follow-up (FUP) scores. Scores from patients receiving routine FUP care were also compiled as a reference population. Results In total, 77 patients attended 1 of 9 workshops. The mean satisfaction score was 9.7 out of 10 for the workshop and 9.96 out of 10 for the moderator. Participants’ baseline mean Patient-Reported Outcomes Measurement Information System (PROMIS) anxiety and depression scores were 57.8 (SD 6.9) and 55.3 (SD 7.5), respectively, which were significantly higher than those of patients receiving routine FUP care (49.1, SD 8.3 and 47.3 SD 8.0, respectively). PROMIS anxiety and depression scores decreased, and the Happiness Index Profile (HIP-10) score—measuring intention and resiliency—increased significantly at 1- and 6-week FUPs. Conclusions The Pathways for Survivors program was favorably received. Anxiety and depression decreased significantly at 1- and 6-weeks after the workshop and remained below baseline at 6 months. Increased HIP-10 scores suggest that patients acquired and implemented skills from the workshop. A 1-day workshop led by a lay moderator significantly improved several psychological measures, suggesting that it may be a useful and time-efficient strategy to improve QOL in breast cancer survivors. We are investigating whether an abbreviated “booster” of the intervention at a later date could further improve and maintain QOL gains.

BACKGROUND Patients with breast cancer frequently experience escalation of anxiety after completing curative treatment. OBJECTIVE This study evaluated the acceptability and psychological impact of a 1-day workshop to emphasize behavioral strategies involving intention and self-efficacy. METHODS Breast cancer survivors who attended a 1-day Pathways for Survivors workshop provided feedback and completed electronic quality of life (QOL) questionnaires at baseline, 1 and 6 weeks, and 6 months after the workshop. Attendees’ baseline QOL scores were compared to follow-up (FUP) scores. Scores from patients receiving routine FUP care were also compiled as a reference population. RESULTS In total, 77 patients attended 1 of 9 workshops. The mean satisfaction score was 9.7 out of 10 for the workshop and 9.96 out of 10 for the moderator. Participants’ baseline mean Patient-Reported Outcomes Measurement Information System (PROMIS) anxiety and depression scores were 57.8 (SD 6.9) and 55.3 (SD 7.5), respectively, which were significantly higher than those of patients receiving routine FUP care (49.1, SD 8.3 and 47.3 SD 8.0, respectively). PROMIS anxiety and depression scores decreased, and the Happiness Index Profile (HIP-10) score—measuring intention and resiliency—increased significantly at 1- and 6-week FUPs. CONCLUSIONS The Pathways for Survivors program was favorably received. Anxiety and depression decreased significantly at 1- and 6-weeks after the workshop and remained below baseline at 6 months. Increased HIP-10 scores suggest that patients acquired and implemented skills from the workshop. A 1-day workshop led by a lay moderator significantly improved several psychological measures, suggesting that it may be a useful and time-efficient strategy to improve QOL in breast cancer survivors. We are investigating whether an abbreviated “booster” of the intervention at a later date could further improve and maintain QOL gains.

Background: Identification of women at elevated risk for highly proliferative, poor prognosis breast cancers could have important implications for screening and prevention. Genome-wide association studies (GWAS) have found >200 single nucleotide polymorphisms (SNPs) associated with breast cancer risk, with many SNPs differentially associated with ER status or intrinsic subtype. We hypothesized that some of these SNPs are preferentially associated with more proliferative tumors, while others are preferentially associated with less proliferative tumors. In this study, we aimed to build a polygenic risk score (PRS) predictive of proliferative tumors, using the GWAS-identified SNPs. Methods: We used data from 3 studies that included array-based SNP genotyping and tumor transcriptomic data: The Cancer Genome Atlas, METABRIC, and the I-SPY 2 Trial (total n=2,467). Our outcome was the risk of recurrence score weighted on proliferation (ROR-P), a validated tumor prognostic signature. Using the breast cancer risk SNPs, we built respective linear regression models to predict ROR-P, with genetic ancestry, study, and ER status as covariates. We performed 5-fold cross-validation and used the model r2 to identify the optimal p-value threshold for including SNPs in the PRS. To decrease uncertainty of our estimates, we performed 100 repeats across the pooled datasets. To test whether this model predicted poor prognosis breast cancers, we first used it to impute ROR-P among genotyped breast cancer cases in UK Biobank (UKB). We then examined the association between “genetically predicted” ROR-P and breast cancer-specific survival using Cox proportional hazards models adjusted for genetic ancestry and age at diagnosis. Results: Associations between 224 breast cancer SNPs and ROR-P were tested. The best-performing model in cross-validation contained 96 SNPs, each associated with ROR-P at p < 0.45, with model r2 0.054. The SNPs with the strongest positive correlations with ROR-P included those discovered in GWAS for HER2-positive and ER-negative cancers, both of which tend to be highly proliferative. Among 7,247 incident cancers in UKB, higher genetically predicted ROR-P was associated with shorter survival, with a per-standard deviation hazard ratio of 1.14 (95% CI 1.05-1.24, p = 0.002). Conclusions: We used breast cancer susceptibility SNPs to construct a PRS fitted to ROR-P, a prognostic signature recapitulating tumor proliferation. This PRS was associated with worse clinical outcomes in breast cancer cases from UKB. Our results suggest that correlations between SNPs and tumor gene expression can be used to “tune” PRS to tumor phenotype, e.g. proliferation. Highly proliferative tumors are more likely to present as advanced cancers even among women getting routine screening. If replicated in other datasets, our findings could be used to identify women who may especially benefit from tailored screening and prevention. Citation Format: Yiwey Shieh, Jacquelyn Roger, Scott Huntsman, Donglei Hu, Jovia L. Nierenberg, Pooja Middha Kapoor, Christina Yau, Gillian Hirst, Laura van 't Veer, Laura Esserman. Development and testing of a polygenic risk score for proliferative breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5883.

Background Transcriptomic immune-related gene signatures have been associated with achievement of pathologic complete response (pCR) and prognosis in the neoadjuvant setting. I-SPY 2 is a multicenter, phase 2 platform trial using response-adaptive randomization within subtypes defined by receptor status (HR/HER2) and MammaPrint (MP) risk to evaluate novel agents as neoadjuvant therapy for women with high-risk breast cancer. Given racial disparities in mortality from breast cancer and the paucity of racial demographic data from clinical trials, we aimed to evaluate the association between racial groups and baseline characteristics, including expression-based subtypes and immune signatures, treatment response, and prognosis of patients enrolled in the I-SPY 2 TRIAL. Methods Our study population included 990 I-SPY 2 patients. 15 patients identified as part of a racial group with Citation Format: Beverly Kyalwazi, Christina Yau, Olufunmilayo Olopade, A. Jo Chien, Anne Wallace, Andres Forero-Torres, Lajos Pusztai, Erin Ellis, Kathy Albain, Anne Blaes, Barbara Haley, Judy Boughey, Anthony Elias, Amy Clark, Claudine Isaacs, Rita Nanda, Hyo Han, Rachel Yung, Debu Tripathy, Kristen Edmiston, Rebecca Viscusi, Donald Northfelt, Qamar Khan, Ashish Sanil, Scott Berry, Smita Asare, Amy Wilson, Gillian Hirst, Nola Hylton, Michelle Melisko, Jane Perlmutter, Hope Rugo, Fraser Symmans, Laura van ‘t Veer, Donald Berry, Laura Esserman. Analysis of clinical outcomes and expression-based immune signatures by race in the I-SPY 2 trial [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 GS4-02.

Background: Liquid biopsies have emerged as effective diagnostic tools in disease monitoring and minimal residual disease detection. Circulating tumor DNA (ctDNA) was recently shown to be a predictor of poor response and recurrence in breast cancer. However, ctDNA shedding from breast tumors can rapidly decrease during treatment, resulting in reduced sensitivity in measuring early changes in tumor response or residual cancer burden (RCB) after neoadjuvant chemotherapy (NAC). We recently reported the discovery of orphan non-coding RNAs (oncRNAs), a class of small RNAs that are not present in healthy cells, but emerge from cancer cells. Similar to ctDNA, tumor-released oncRNAs can be used to detect the presence of an underlying tumor; however, since they are actively released by cancer cells, their abundance in the cell-free compartment is substantially higher than ctDNA. Therefore, we hypothesized that monitoring circulating oncRNAs in blood permits a more sensitive approach to measuring treatment response (i.e., pathologic complete response, or pCR) and estimating RCB. Patients and Methods: Cell-free RNA (cfRNA) was extracted from ~1 ml sera of 72 breast cancer patients treated in the neoadjuvant I-SPY 2 TRIAL with NAC alone or combined with MK-2206 (AKT inhibitor) treatment. For each patient, treatment-naïve samples (T0) were compared with samples from post-treatment and prior to surgery (T3) time-point. RNA samples were subjected to small RNA sequencing (SMARTer), and the presence and abundance of cell-free oncRNA species were then determined by identifying and counting the reads that map to oncRNA loci across samples. Notably, oncRNAs species were pre-annotated from the Cancer Genome Atlas (TCGA), and our approach does not require bespoke personalized assays. We used a machine-learning model to compare abundance of cfRNA species before and after treatment (i.e., T3-T0) to predict pCR and RCB. For this, we split our cohort into a training and a testing set (48 and 24) and trained a model to simultaneously learn the presence of residual disease (pCR vs. no pCR) and its extent (RCB). We then measured the performance of our model on the held-out test data and the entire dataset. To confirm the robustness of our model, we also employed a leave-one-out strategy, whereby pCR and RCBIndex of each patient was predicted using a model that was trained on the other patients in the cohort. Finally, to assess the ability of our oncRNA-based model to risk-stratify patients who fail to achieve pCR (without having been explicitly trained on relapse data), we used the model’s oncRNA score to predict patients at the highest risk of distant recurrence (n=8 out of 36) and performed a multivariate Cox analysis, controlling for HR/Her2 status (median follow-up time was 4.8 years). Results: The model’s accuracy for predicting pCR—based on changes in circulating oncRNA species between T3 and T0—was 85% for the training data and 79% for the held-out test data (positive predictive value of 75% and negative predictive value of 83%) with combined accuracy of 83%; precision 86% and recall 83%; Pearson R=0.5 for RCB. A leave-one-out strategy showed similar performance (area under ROC of 0.77 versus 0.81 in train-test split). Finally, among the patients who failed to achieve pCR, we observed a significantly higher risk of distant recurrence in those with the highest scores (DRFS: hazard-ratio = 8.4, ANOVA P Citation Format: Hani Goodarzi, Albertas Navickas, Jefferey Wang, Kristle Garcia, Mark J Magbanua, Lisa Fish, Lamorna Brown Swigart, Gillian Hirst, Denise Wolf, Christina Yau, Jo Chien, Carol Simmons, Amy Delson, Laura Esserman, Laura van 't Veer. Tumor-released circulating orphan non-coding RNAs reflect treatment response and survival in 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 PD9-04.

Background: The I-SPY2 TRIAL has shown that the addition of pembrolizumab to standard neoadjuvant chemotherapy results in improved rates of estimated pathologic complete response (pCR) for hormone-receptor positive (HR+) as well as triple negative breast cancer (TNBC). I-SPY2 has tested a number of novel immunotherapy combinations including the combination of pembrolizumab and SD-101, a synthetic oligonucleotide with cytidine-phospho-guanosine (CpG) motifs that stimulates plasmacytoid dendritic cells (pDC) through engagement of toll-like receptor 9 (TLR9). Biomarkers of response to immunotherapy may be different than chemotherapy, and pathologic response may not fully reflect the benefit from checkpoint inhibitors. Early markers of response to immunotherapy are needed to minimize the risk of immune-related toxicity in patients who are unlikely to benefit. The objective of this study is to assess the change in regional lymph nodes (LNs) by breast MRI in I-SPY2 patients receiving neoadjuvant chemotherapy +/- immunotherapy, and to explore if changes in regional LNs correlate with pCR and residual cancer burden (RCB). Methods: This is a retrospective study of the prospective multicenter I-SPY2 adaptive neoadjuvant trial investigating all patients enrolled at UCSF in 3 study arms between Dec 2015 and April 2021: 1) Control (weekly paclitaxel 80 mg/m2 x 12 weeks followed by AC x 4); 2) weekly paclitaxel + pembrolizumab 200 mg IV every 3 weeks, followed by AC x 4; 3) weekly paclitaxel + every 3 week pembrolizumab + intra-tumoral SD-101 weekly x 4 then every 3 weeks x 2 followed by AC x 4. Serial pre-operative breast MRIs were performed in all patients at baseline, 3 weeks, 12 weeks, and 20 weeks. A single breast radiologist blinded to treatment arm reviewed all MRIs for all patients included in this study and assessed longest diameter and cortical thickness of the largest ipsilateral axillary LN, number and location of abnormal LNs, and development of new abnormal LNs over time. Rates of pCR and RCB were evaluated in patients who showed evidence of LN growth and/or development of new lymphadenopathy (LAD) compared to those who did not. A two-sample test for equality of proportions to measure the statistical significance at alpha=.5 between control and immunotherapy arms and LN change was used. Results: A total of 43 patients were included, of whom 16 were in the control group, 11 received pembrolizumab, and 16 received pembrolizumab + SD-101. Median age was 45 years, mean tumor size was 4.8 cm, and 60% of tumors were HR+HER2-negative with the remaining 40% being TNBC. Baseline patient and tumor characteristics were similar between the 3 study arms. LN enlargement and/or development of new LAD over time was significantly more common in patients receiving immunotherapy than patients in the control arm (48.1% versus 6.3%, p=0.006). This was seen in both HR+ and TN subtypes. While there was a numerically higher rate of pCR/RCB-1 pathology in patients with increased and/or new LAD compared to those without (64% vs 51%), this difference was not statistically significant. The association of LN change and immune-related toxicities will be reported. Conclusion: The addition of immunotherapy to standard neoadjuvant chemotherapy in the I-SPY2 trial was associated with an increase in size of ipsilateral axillary LN and/or development of new LAD on serial breast MRI imaging during the course of neoadjuvant treatment. These changes were not associated with worse pathologic response at surgery and should not be assumed to be due to disease progression. Whether these changes could reflect immunotherapy benefit needs to be investigated in a larger trial with longer follow-up. Citation Format: Anika Christofferson, Elissa Price, Rita A Mukhtar, Amrita Basu, Laura Esserman, A Jo Chien. Single-institution retrospective analysis of lymph node (LN) change on breast MRI in patients with high risk early-stage breast cancer receiving neoadjuvant chemotherapy with and without immunotherapy on the ISPY-2 TRIAL [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 P3-03-07.