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Multiple myeloma (MM) is a highly refractory hematologic cancer. Targeted immunotherapy has shown promise in MM but remains hindered by the challenge of identifying specific yet broadly representative tumor markers. We analyzed 53 bone marrow (BM) aspirates from 41 MM patients using an unbiased, high-throughput pipeline for therapeutic target discovery via single-cell transcriptomic profiling, yielding 38 MM marker genes encoding cell-surface proteins and 15 encoding intracellular proteins. Of these, 20 candidate genes were highlighted that are not yet under clinical study, 11 of which were previously uncharacterized as therapeutic targets. The findings were cross-validated using bulk RNA sequencing, flow cytometry, and proteomic mass spectrometry of MM cell lines and patient BM, demonstrating high overall concordance across data types. Independent discovery using bulk RNA sequencing reiterated top candidates, further affirming the ability of single-cell transcriptomics to accurately capture marker expression despite limitations in sample size or sequencing depth. Target dynamics and heterogeneity were further examined using both transcriptomic and immuno-imaging methods. In summary, this study presents a robust and broadly applicable strategy for identifying tumor markers to better inform the development of targeted cancer therapy. Significance: Single-cell transcriptomic profiling and multiomic cross-validation to uncover therapeutic targets identifies 38 myeloma marker genes, including 11 transcribing surface proteins with previously uncharacterized potential for targeted antitumor therapy.

Background: Galectins are sugar binding proteins that play a role in adhesion, apoptosis, immune regulation, and many other cellular processes. There are three different classes of galectins, and they are all found intracellularly and secreted in serum. Galectins have an established relationship with breast cancer, and galectin-3 has been repeatedly associated with cancer cell survival and tumor progression. Most research regarding breast cancer and galectins has used immunohistochemistry (IHC) as a method for identifying galectin expression in breast cancer tissue samples. However, little research has identified a relationship between serum galectin concentrations and breast cancer subtypes. Breast cancer is characterized both by histological and molecular subtype, and this identification often directs treatment decisions. The current method for identifying breast cancer subtypes is through invasive biopsy and the subsequent use of IHC. This project characterized serum galectin concentrations in breast cancer patients to determine if they changed based on different histological and molecular subtypes, cancer stage, and other patient characteristics. Our goal was to evaluate a potential noninvasive means of breast cancer subtype identification and to identify potential therapeutic targets. Methods: One-hundred breast cancer patient serum samples were studied using Enzyme-linked Immunosorbent Assays (ELISAs) to determine concentrations of galectins -1, -3, -7, and -9. Results were compared using many patient characteristics, including breast cancer subtype, stage, and patient history (smoking status and treatment). Statistical Analysis was performed using ANOVA, Student’s t-test, and the Wilcoxon Method. Results: The concentrations of galectins -1, -3, and -9 in breast cancer patients were all significantly higher than those of healthy controls (Table 1), which is consistent with previous studies. The concentration of galectin-3 was significantly higher in invasive lobular carcinoma samples (N, 6; mean, 13.04 ng/mL) compared to invasive ductal carcinoma samples (N, 80; mean, 9.93 ng/mL; p-value, 0.0428). Galectin-3 concentrations were significantly lower in samples from breast cancer patients who received chemotherapy (N, 9; mean, 9.22 ng/mL) versus those who did not (N, 7; mean, 14.60 ng/mL; p-value, 0.0228). Concentrations of galectin-1 were found to increase by stage (p-value, 0.0031), with significant differences between samples from patients with stage I breast cancer (N, 45; mean, 19.02 ng/mL) and both stage II (N, 40; mean, 24.15 ng/mL; p-value, 0.0127) and stage III (N, 12; mean, 28.37 ng/mL; p-value, 0.0026) disease. Conclusions: Our findings suggest a potential use for serum galectin-3 concentrations as a non-invasive means for breast cancer histological subtype differentiation and more refined diagnosis. In addition, our results suggest a possible use of galectin-1 concentrations for more accurate cancer staging. Further research could explore the relationship of serum galectin concentrations and other breast cancer subtypes. Future studies could also analyze how galectin concentrations change with patient treatment status and determine the potential of galectins as specific targets for breast cancer treatment. Table 1: Galectin Concentrations in Breast Cancer vs Healthy Controls Citation Format: Jonah Shealy, Alex Kesic, Avery Funkhouser, Julie Martin, W. Larry Gluck, w. Jeffery Edenfield, Anna Blenda. Analysis of Serum Galectin Profiles by Breast Cancer Subtypes and Patient Characteristics [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 P2-23-18.

CONTEXT: Endocrine therapy combined with CDK4/6 inhibitor is the standard frontline treatment for the vast majority of HR+/HER2- metastatic breast cancer (MBC) patients. Despite an overall survival benefit, patients eventually progress and mechanisms of resistance to this combination are not well identified. Non-invasive monitoring of the efficacy of treatment could help into tailoring therapeutic regimen. Extracellular vesicles (EVs) are a group of heterogeneous nanosized bioparticles (30-1000nm), released by almost all cell types - including tumor, platelets, and immune cells – carrying informative biological material emanating from the mother cell and circulating in the blood stream. In this project, we ambition to assess whether the vesiclemia, i.e. plasmatic extracellular vesicle concentration can be used as a clinic-biological parameter to assist in the monitoring of patients. METHODS: EPICURE is an ongoing pilot prospective cohort study of heterogeneous and massive data integration, i.e. multi-omics approaches in MBC patients. The present study focused on patients with HR+/HER2- MBC receiving frontline endocrine therapy+iCDK4/6. Plasma samples were drawn every 3 months during the treatment until progression. The workflow for the enrichment of circulating EVs was developed from frozen plasma. A semi-automatized isolation procedure using size exclusion chromatography combined with the newly developed interference light microscopy apparatus Videodrop allowed to routinely separate plasmatic EVs and quantify vesiclemia in a fast and reliable manner for a large number of samples (longitudinal follow-up of MBC patients). RESULTS: 26 patients were included and monitored for vesiclemia. Median age was 58.5y (±13.7). Metastatic disease sites were distributed as follows: bone metastases (21; 84%), liver (21; 84%), thoracic (10; 40%), node (2; 8%), brain (1; 4%), others (2; 8%). Endocrine therapy included aromatase inhibitors (20; 77%), fulvestrant (6; 29%), GnRH agonists (5; 19%) and CDK4/6 inhibitors palbocilib (15; 57%), abemaciclib (8; 31%) and ribociclib (3; 11%). With a median follow-up time of 22.1 months (95%CI 21.2 - not reached), median progression free survival was 21.8 months (95%CI 18.1 - not reached). Median time on treatment was 19.4 months (IQR 11.6 - 22.1). Objective response rate was confirmed in 12 patients (6 with complete response). Out of the 26 patients, 12 stopped the frontline treatment due to disease progression. 135 longitudinal follow-up samples were analyzed for EVs. All patients who progressed rapidly after treatment initiation (i.e median PFS< 6 months) had an increased vesiclemia at the months 2 and 6 after inclusion. Conversely, patients who had a median PFS >18m had a stable vesiclemia during this period. CONCLUSION This study aims to use circulating EVs as a therapeutic companion to anticipate treatment resistance and tumor progression in MBC patients. Our preliminary data suggest that the vesiclemia could be used as a predictive tool to anticipate treatment failure, and thus might be used to tailor treatments in time. Citation Format: Mathilde Richard, Jean Sebastien FRENEL, Laurent Mathiot, Mario Campone, Mathilde Colombie, Marie Robert, Anne Patsouris, Frederic Bigot, Julie Gavard, Gwennan André-Grégoire, Laetitia Guevel. Extracellular vesicle-based biomarker assay for the monitoring of the efficacy of frontline endocrine therapy + CDK4-6 inhibitors in metastatic 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 P3-11-09.

Purpose: To determine the rate of rib fracture in a cohort of patients with breast cancer treated with proton therapy and enrolled on a prospective registry. In series investigating photon therapy for breast cancer, the rib fracture rate ranges from 0.3-13% Methods: From a prospective database, we identified patients treated with proton therapy for breast cancer at our institution between January 1, 2012 and December 31, 2020. Clinical and dosimetric data was extracted from the electronic medical record. The cumulative incidence method assessed rib fracture rate; the Fine-Gray test statistic assessed prognostic significance select variables. Results: 225 patients were identified, 223 women and 2 men. Median age at the time of radiation was 57.8 years (range, 25 – 87). 26% of patients were black, 69% white and 5% were other races or race not disclosed. 5% were Hispanic. 74% of patients had left-sided breast cancer, 5% bilateral, and 21% right-sided. DEXA scan was normal in 20%, showed osteopenia in 34%, osteoporosis in 6%, and not performed in 40%. 57% of patients received antiendocrine therapy with an aromatase inhibitor. For 16% of patients, the breast +/- internal mammary nodes (IMN) were treated, while 32% underwent proton therapy to treat the breast and comprehensive regional lymphatics. 1% of patients had chest wall +/- IMN treated, while 51% underwent proton therapy to treat the chest wall and comprehensive regional lymphatics. 41% of patients were treated with passive scatter proton therapy (n=92); 52% of these had mastectomy. 58% of patients received treatment with pencil beam scanning (PBS) proton therapy (n=131); 53% of these had mastectomy. A combination of passive scatter and PBS was used for 2 patients (1%). 85% of patients received a boost. Median follow-up was 3.1 years (range, 0.2 – 9.1). 97% of patients had > 12 months of follow-up. The 3 year cumulative incidence of in-field rib fracture was 3.7% (95%CI: 1.6%-7.1%). In total, 8 patients developed in-field rib fractures, one symptomatic and 7 identified incidentally on surveillance imaging, for a 0.4% rate of symptomatic rib fracture. Median time from completion of radiation to identification of rib fracture was 1.8 years (range, 0.4-7.4 years). Rib fractures occurred within 2.2 years from radiotherapy completion for seven of the eight patients who experienced this side effect. Three patients developed rib fractures outside of the radiation field, for a cumulative incidence of out-of-field rib fracture of 0.9% (95%CI: 0.2-3.0%). No variables were associated with rib fracture on univariate analysis. Of those with in-field rib fractures, 3 had low and 3 had normal bone density while 2 had not undergone testing; of those with out-of-field rib fractures, 2 had osteopenia and 1 did not have testing. Conclusions: Although a proton beam has higher biological dose deposition at end-of-range than the assumed constant RBE=1.1, the 3 year rate of any in-field rib fractures in our series remains low at 3.7%, with a 0.4% rate of symptomatic rib fracture. Contouring ribs as an OAR and establishing a dose constraint warrants further investigation as a means to maintaining a low rate of rib fracture with proton therapy. Citation Format: Julie Bradley, Xiaoying Liang, Raymond Mailhot Vega, Chunbo Liu, Eric Brooks, Teena Burchianti, Emma Viviers, Roi Dagan, Oluwadamilola Oladeru, Christopher Morris, Nancy Mendenhall. Incidence of rib fracture following treatment with proton therapy for 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 P1-10-08.

Introduction: Breast cancer has pioneered precision medicine with prognostic and predictive subtypes, defined by immunohistochemistry (IHC). Novel therapeutic strategies have led to the emergence of HER2-Low (H2L) as a new entity, defined as tumors with HER2 IHC score of 1+ (>10% cell stained), as well as those with 2+ (>10% cell stained) with paired negative in-situ hybridization (ISH) assay. H2L has been reported to represent up to half of all breast cancer. Further investigation into the mutational landscape of H2L compared to historical subtypes is needed to understand the clinical and biologic factors driving mechanisms of resistance and to consider post-progression treatment options within H2L populations. Methods: The Caris Life Sciences database was used to identify H2L breast tumors by IHC and CISH and evaluated for mutations detected by DNA next-generation sequencing (NextSeq 592-gene panel or NovaSeq whole exome panel). PD-L1 expression was tested by IHC (SP142 IC ≥ 1%). Tumor mutational burden (TMB) was measured by totaling somatic mutations per tumor (high ≥ 10 mutations per Mb). Statistical significance was determined using Fisher’s-Exact/Mann Whitney/X2 test with Benjamini-Hochberg-correction-adjusted p value (q value) of Citation Format: Rani Bansal, Julie McGrath, Phil Walker, Matias A. Bustos, Estelamari Rodriguez, Sarah L. Sammons, Melissa K. Accordino, Jane Meisel, Margaret Gatti-Mays, Emily Hsu, Kate I. Lathrop, Virginia Kaklamani, Matthew Oberley, W. Michael Korn, Stephanie L. Graff. HER2-12 Genomic and Transcriptomic Landscape of HER2-Low 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 HER2-12.

Background: Combination chemotherapy (CT) remains a standard of care in advanced breast cancer (ABC) with aggressive disease features (rapidly progressing or highly symptomatic disease, including life-threatening visceral crisis). To date, no data have been published on a head-to-head comparison of CDK4/6 inhibitor (CDK4/6i) + endocrine therapy (ET) vs combination CT in this patient (pt) population. RIGHT Choice, a randomized, open-label, multi-national, Phase II trial, investigated the efficacy and safety of first-line ribociclib (RIB) + ET vs combination CT in pre/perimenopausal pts with HR+/HER2− ABC with aggressive disease (where combination CT is clinically indicated by physician’s judgment). Here we report the results of the primary endpoint of progression-free survival (PFS) and key secondary endpoints from this study. Methods: Pre/perimenopausal pts with HR+/HER2− ABC (>10% estrogen receptor–positive [ER+]) and no prior systemic therapy for ABC were randomized 1:1 to receive either RIB (600 mg daily, 3 weeks on/1 week off) with letrozole/anastrozole + goserelin or investigator’s choice of CT (docetaxel + capecitabine, paclitaxel + gemcitabine, or capecitabine + vinorelbine). Randomization was stratified by presence of liver metastases and whether the disease-free interval (duration from date of complete tumor resection for primary breast cancer lesion to the date of documented disease recurrence) was less than two years. Pts included in the trial had ABC not amenable to curative therapy for which combination CT was clinically indicated by physician’s judgment (i.e., symptomatic visceral metastases, rapid progression of disease or impending visceral compromise, or markedly symptomatic non-visceral disease). Median PFS (mPFS) and median time to treatment failure (mTTF) were evaluated by Kaplan-Meier methods. Overall response rate (ORR) was also analyzed, with quality of life and biomarker analyses planned. RIGHT Choice is registered at ClinicalTrials.gov (NCT03839823). Results: A total of 222 pts (112 RIB + ET; 110 CT) were enrolled from Feb 2019 to Nov 2021. Pts with symptomatic visceral metastases (n=150; 67.6%), rapid disease progression (n=41; 18.5%), and markedly symptomatic non-visceral metastases (n=31; 14.0%) were included. Overall, 116 pts (52.3%) had visceral crisis based on guideline definitions. A majority of pts (n=190; 85.6%) had tumors that were ≥50% ER+. At data cutoff (Apr 12, 2022), median follow-up was 24.1 mo; 45.5% and 23.6% of pts remained on treatment in the RIB + ET arm and combination CT arm, respectively. The primary endpoint was met, with a statistically significant PFS benefit of ≈1 year for RIB + ET vs combination CT (mPFS, 24.0 vs 12.3 mo; hazard ratio, 0.54; 95% CI, 0.36-0.79; P=.0007). OS data were immature at data cutoff. The mTTF was ≈10 mo longer for RIB + ET vs CT (18.6 vs 8.5 mo; hazard ratio, 0.45; 95% CI, 0.32-0.63). The ORR was similar for RIB + ET vs CT (65.2% vs 60.0%). No new safety signals were observed in pts on RIB. Lower rates of treatment-related serious adverse events (AEs; 1.8% vs 8.0%) and lower rates of discontinuation due to treatment-related AEs (7.1% vs 23.0%) were seen with RIB + ET vs CT, respectively. AEs observed with combination CT were consistent with the published data. Conclusions: This analysis demonstrated a statistically significant and clinically meaningful PFS benefit with RIB + ET over combination CT in the first-line pre/perimenopausal pt population with aggressive HR+/HER2− ABC disease. This is the first study comparing a CDK4/6i + ET vs combination CT and demonstrating the superiority of RIB + ET in aggressive HR+/HER2− ABC. This evidence supports RIB+ ET use as a preferred option for this pt population. Citation Format: Yen-Shen Lu, Eznal Izwadi Bin Mohd Mahidin, Hamdy Azim, Yeşim ERALP, Yoon-Sim Yap, Seock-Ah Im, Julie Rihani, James Bowles, Teresa Delgar Alfaro, Jiwen Wu, Melissa Gao, Khemaies Slimane, Nagi El Saghir. Primary results from the randomized Phase II RIGHT Choice trial of premenopausal patients with aggressive HR+/HER2− advanced breast cancer treated with ribociclib + endocrine therapy vs physician’s choice combination chemotherapy [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 GS1-10.

Background PD-1 inhibitors have shown significant efficacy in triple negative breast cancer (BC), however, durable responses are less common in estrogen receptor-positive (ER+) BC. Better markers are therefore needed that will identify likely responders to PD-1 inhibitors among patients with luminal BC. While most efforts have focused on the immune checkpoint protein PD-L1, the alternative PD-1 ligand, PD-L2, has been largely overlooked. We aimed to determine if PD-L2 is associated with unfavorable prognosis in ER+ BC. Methods PD-L2 protein levels in cancer cells and stromal cells were measured retrospectively by quantitative immunofluorescence histocytometry in tissue microarrays of therapy-naïve, localized or locoregional ER+ BC and correlated with progression-free survival (PFS). Evaluable tumor PD-L2 data were derived from a main study cohort A diagnosed between 1988-2005 (n=684) with extensive clinical and outcome data and from an independent validation cohort B diagnosed between 1992-2012 (n=273). Patients received standard-of-care adjuvant therapy without immune checkpoint inhibitors after tumor resection. Results Univariate analysis of the main cohort A revealed that high PD-L2 expression in cancer cells was associated with shorter PFS (HR=1.8; 95%CI:1.3-2.6; p=0.001), an observation that was validated in an independent cohort B (HR=2.3, 95%CI:1.1-4.8; p=0.026). Approximately one third of ER+ BC cases were classified as high PD-L2. After multivariable adjustment for common clinicopathological variables, high cancer cell levels of PD-L2 remained independently predictive of early recurrence (HR=2.0; 95%CI:1.4-2.9; p< 0.001). Sub-analysis of ER+ BC cases treated with adjuvant chemotherapy (n=197) suggested that high PD-L2 levels in cancer cells was associated with particularly increased risk of progression (multivariable HR=3.4; 95%CI:1.9-6.2; p< 0.001). The observed frequent expression of PD-L2 protein in BC provided scientific rationale for the design of our ongoing phase II clinical trial (NCT04243616) of neoadjuvant combined PD-1 inhibitor (cemiplimab; Regeneron Pharmaceuticals Inc) and chemotherapy in patients diagnosed with PD-L1+ and/or PD-L2+ BC. The primary objective of this trial is to assess pathologic responses to neoadjuvant treatment with secondary objective of assessing the correlation between PD-L1/PD-L2 status and tumor responses. Pathologist review of PD-L1 and PD-L2 expression in an initial set of ER+ tumors (n=15) screened for trial eligibility revealed frequent discordance between cancer cell positivity for PD-L1 and PD-L2 protein (PD-L1: median=0%; range 0-2% vs. PD-L2: median=18%; range < 1-60%) as well as immune cell positivity (PD-L1: median=5%; range 0-50% vs. PD-L2: median=0; range 0-50%). Conclusions In treatment-naïve ER+ breast tumors, high cancer cell expression of PD-L2 protein was an independent predictor of poor clinical outcome, with evidence of further elevated risk of progression in patients who received adjuvant chemotherapy. Preliminary analyses of ER+ tumors from our ongoing clinical trial showed frequent discordance between baseline PD-L1 and PD-L2 protein expression in both cancer cells and immune cells. Collectively, our analyses indicate that PD-L2 has prognostic value for ER+ BC, and our progress justify further studies to determine whether PD-L2, alone or in combination with PD-L1, may serve as a predictive marker of response to PD-1 inhibitors. Citation Format: Lubna N. Chaudhary, Inna Chervoneva, Amy R. Peck, Yunguang Sun, Misung Yi, John F. Langenheim, Julie M. Jorns, Sailaja Kamaraju, Yee Chung Cheng, John Burfeind, Christopher R. Chitambar, Jeffrey A. Hooke, Albert J. Kovatich, Craig Shriver, Hai Hu, Juan P. Palazzo, Marluce Bibbo, Terry Hyslop, Richard Pestell, Edith P. Mitchell, Hallgeir Rui. High PD-L2 Protein Expression in Cancer Cells is an Independent Marker of Unfavorable Prognosis in Luminal Breast Tumors [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 P2-11-13.

Introduction: Breast cancer treatment is associated with cancer-related cognitive impairment (CRCI). However, the differential effect of endocrine therapy (ET) vs chemotherapy followed by endocrine therapy (CET), including the impact of menopausal status, on CRCI is not well understood. Methods: Participants (pts) with hormone receptor positive, HER2 negative breast cancer with 1-3 positive lymph nodes and an Oncotype DX recurrence score of 0-25 enrolled in the RxPONDER trial were randomly assigned to ET alone versus CET. Until the health-related quality of life (HRQoL) accrual goal was reached, English speaking pts in the US were invited to complete HRQoL questionnaires including the 8-item PROMIS Perceived Cognitive Function Concerns (PCF) Short Form questionnaire shortly after randomization (baseline), as well as 6, 12, and 36 months after baseline. Analysis of measures of anxiety and fatigue is presented separately. Standardized T scores (mean 50; SD 10) for PCF were computed with higher scores indicating less cognitive impairment. The primary endpoint of this exploratory analysis was to compare mean PCF T scores by treatment arm and menopausal status. Separately by menopausal status, a generalized estimating equations (GEE) model was fit to the three timepoints adjusting for baseline to estimate the difference between treatment arms and whether there was a time trend over the three follow-up measures. Results: The HRQoL accrual exceeded the goal of 500 patients, with 74% of pts participating voluntarily until the QOL invitation was removed from the protocol (Dec 1, 2012). A total of 139 pre and 429 postmenopausal pts completed the questionnaires at baseline. T scores were similar between ET and CET arms at baseline [Table 1]. In the ET arm, T scores decreased from baseline to 6 and 12 months but recovered to baseline at 36 months. In the CET arm, T scores decreased from baseline to 6 months and 12 months but did not return to baseline at 36 months. The mean score difference between CET and ET over time was -3.02 (p=0.01) and -2.36 (p=0.003) for pre and postmenopausal pts, respectively. Adjusting for baseline, there was no significant time trend over the three follow-up periods for either premenopausal (p=0.12) or postmenopausal (p=0.49) pts. Dropoff occurred over time with 79%, 76%, 60% of pts at baseline participating at 6, 12, and 36 months. Complete endocrine treatment adherence data are not yet available at each timepoint. Conclusion: Chemoendocrine therapy has a greater negative effect on patient-reported CRCI compared to ET alone in both pre- and post-menopausal pts and it is sustained over 36 months. Interventions to prevent or treat CRCI are needed to improve the long-term quality of life of patients treated with CET. Table 1. Comparisons of mean Cognitive Function score by treatment arm and menopausal status. Citation Format: Irene Kang, Jamie K. Forschmiedt, Michelle M. Loch, William E. Barlow, Danika L. Lew, Julie R. Gralow, Funda Meric-Bernstam, Kathy S. Albain, Daniel F. Hayes, Nancy U. Lin, Edith A. Perez, Lori J. Goldstein, Priya Rastogi, Anne F. Schott, Steven Shak, Priyanka Sharma, Jieling Miao, Debu Tripathy, Lajos Pusztai, Gabriel N. Hortobagyi, Kevin Kalinsky, N. Lynn Henry. Patient-reported cognitive impairment in women participating in the RxPONDER trial (SWOG S1007) by menopausal status [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 GS1-04.

Background: For patients who are node positive at presentation and are found to have a complete nodal tumour response (ypN0) post-neoadjuvant chemotherapy (NACT), we do not yet know whether local axillary therapy can be modified based on the response to NACT. ATNEC addresses whether axillary treatment can be de-escalated, post-surgery, in T1-3N1M0 breast cancer patients who have no residual nodal disease post-NACT. Methods: Design: ATNEC is a phase III, randomized (1:1), multi-centre trial, with embedded economic evaluation. Patients with proven axillary node metastases on needle biopsy receive NACT followed by sentinel node biopsy (SNB). If the sentinel nodes have converted to ypN0, ATNEC randomizes patients to axillary treatment (nodal radiotherapy [ART] or axillary nodal clearance [ANC]) vs. no further axillary treatment. Stratification: Institution, type of surgery (breast conserving surgery vs mastectomy), receptor status (triple negative vs HER2 positive vs ER positive and/or PR positive and HER2 negative). Inclusion criteria: • Age ≥ 18 • Male or female • T1-3N1M0 breast cancer at diagnosis (pre-NACT) • FNA or core biopsy confirmed axillary nodal metastases at presentation • ER and HER2 status evaluated on primary tumour • Received standard NACT as per local guidelines • Imaging of the axilla to assess response to NACT • Dual tracer SNB post-NACT and at least 3 nodes removed (sentinel nodes and marked node). o If a single tracer is used, the patient is eligible if the involved node is marked pre-NACT and at least 3 nodes removed (including the marked node) o If axillary node sampling is performed following failed localization of sentinel nodes, patient is eligible if at least 3 nodes removed (including the marked node). o If node is not marked, or marked node is not removed, patient is eligible if the histology report shows evidence of down-staging with complete pathological response in at least one node of the 3 removed nodes. • No evidence of nodal metastases post-NACT (ypN0) Exclusion criteria: • Bilateral invasive breast cancer • SNB prior to NACT • Previous ipsilateral axillary nodal surgery • Previous cancer within last 5 years or concomitant malignancy Aims: To assess whether omitting further axillary treatment (ART or ANC) for patients with early stage breast cancer and axillary nodal metastases on needle biopsy - who post NACT have no residual nodal disease on SNB (ypN0) - is non-inferior to axillary treatment in terms of disease-free survival, and whether lymphoedema is reduced at 5 years. Statistical methods: All analyses will be carried out on an intention-to-treat basis to preserve randomization, avoid bias from exclusions and preserve statistical power. Radiotherapy Quality Assurance: ATNEC has in-built radiotherapy QA coordinated by National Radiotherapy Trials QA (RTTQA) group. The RTQA monitors trial protocol compliance ensuring clinical outcomes reflect differences in randomization schedules rather than departures from the protocol. ATNEC is the only trial in the UK that offers QA for IMC radiotherapy. Screening Data: ATNEC collects screening data to monitor acceptance rates and reasons why patients decline the trial to identify ways to improve recruitment. Screening data until 30-Jun-22 shows that 69% of eligible patients were approached (244/354) and, of those approached, 45% were consented (109/244). For the 81 patients who declined, the most common reasons were; preference for axillary treatment (31%), preference for no axillary treatment (10%), no reason documented (23%) and ineligibility (21%). ClinicalTrials.gov: NCT04109079 Target accrual: 1900 Target sites: 100 Trial Status: Recruiting. As of 30-Jun-22: 52 sites open, 158 patients enrolled, 54 randomised. ATNEC is open to new sites and international collaboration. Citation Format: Amit Goyal, Sophie Nicholls, Andrea Marshall, Natalie Hammonds, Duncan Wheatley, Beatrix Elsberger, Janice Rose, Helen-Teresa Edwards, Roeum Butt, Abeer Shaaban, Shama Puri, Samreen Ahmed, Tara Homer, Luke Vale, Julie Bruce, Sophie J. Gasson, Helen Higgins, Janet A. Dunn. ATNEC: A multicentre, randomized trial investigating whether axillary treatment can be avoided in T1-3N1M0 breast cancer patients with no residual cancer in the axillary lymph nodes after neoadjuvant chemotherapy [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 OT1-09-02.

Background: HER2-positive versus HER2-negative ductal carcinoma in situ (DCIS) of the breast has been associated with an increased risk of local recurrence after breast-conserving surgery (BCS) and radiotherapy (RT). In recognition of this, the NASBP-B43 trial was designed to determine if two doses of trastuzumab would improve local control with BCS plus RT in HER2-positive DCIS. The trial demonstrated a non-statistically significant advantage with the addition of trastuzumab in reducing ipsilateral breast recurrence (IBR). The predictive 7-gene DCIS biosignature, DCISionRT with Residual Risk Subtype (PreludeDxTM, Laguna Hills, CA) has been shown to classify DCIS patients into two distinct groups of patients with substantially different rates of IBR following BCS plus RT. Based upon these differences in outcome, we assessed the IBR rate in patients with HER2(+) DCIS treated with BCS and RT who were or were not in the Residual Risk Subtype group defined using DCISionRT, while accounting for the varying clinicopathologic profile of the patients. Materials & Methods: DCISionRT was evaluated in a subset of 178 women with HER2(+) DCIS treated with BCS and RT as part of a multinational cohort of 926 patients from the United States, Sweden, and Australia, who were used in the validation studies for DCISionRT. Central pathology review and biosignature testing were performed at a CLIA-certified lab (Laguna Hills, CA). HER2(+) DCIS was defined as patients with a HER2(3+) immunohistochemistry >10% per ASCO/CAP guidelines. The IBR rate was calculated for the overall group of HER2(+) patients and those in the Residual Risk group. Individual patient outcome and biosignature results were analyzed using Kaplan Meier and Cox Proportional Hazard analyses. Results: The biosignature classified 113 of the 178 (63%) HER2(+) women into the Residual Risk group (DS>2.8 with RRt). Patients in the Residual Risk group had a significantly greater IBR (HR=8.3; 95%CI: 1.1,50, p=.012) over 10-years, with a corresponding 10-year total IBR rate of 16.2% (95%CI: 9.7%, 26.5%) versus 1.6% (95%CI: 0.2%, 10.9%) for all other HER2(+) patients. In univariate analysis, younger patients tended to have higher IBR rate after BCS plus RT, but only Residual Risk was significantly associated with IBR rate after BCS plus RT. Moreover, multivariable analysis demonstrated that the Residual Risk group was eight times more likely to recur after BCS and RT, while clinicopathologic factors (age, grade, tumor size) were not associated with higher IBR rates. Conclusion: The DCISionRT Residual Risk group was predictive for 10-year IBR risk after BCS plus RT in women with HER2(+) DCIS. Approximately 40% of patients with HER2(+) DCIS would be expected to achieve low rates of recurrence with BCS and RT, while about 60% of these women (classified in the Residual Risk group) would have higher recurrence rates and may benefit from further therapy, such as HER2-directed therapies. These findings suggest that if the results of the B43 trial were re-analyzed using the predictive 7-gene biosignature (DCISionRT with Residual Risk Subtype), better clarity could be gained on the true impact of trastuzumab on IBR rates in patients with HER2(+) DCIS and the patients most likely to benefit from this additional therapy. Table 1. Univariate and Multivariable Cox Proportional Hazards Analyses. Citation Format: Frank Vicini, Chirag Shah, Rachel Rabinovitch, Pat Whitworth, Julie A. Margenthaler, Brian J. Czerniecki, DAVID J. DABBS, Sheila Weinmann, Michael Leo, G Bruce Mann, Fredrik Wärnberg, jess Savala, Steven C. Shivers, Karuna Mittal, Troy Bremer. Characterization of recurrence risk after lumpectomy and radiotherapy in HER2-positive ductal carcinoma in situ of the breast, using 7-gene predictive biosignature: Implications for the NSABP-B43 trial results [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 P1-04-06.

Clonal hematopoiesis of indeterminate potential after (neo)adjuvant chemotherapy versus endocrine therapy for early breast cancer: the CIRCE-eBC prospective cohort study Background: Clonal hematopoiesis of indeterminate potential (CHIP) is an age-related condition associated with higher risk of hematologic malignancies, cardiovascular disease, and all-cause mortality. Patients (pts) with early breast cancer (eBC) receiving chemotherapy (CT) have increased risk of treatment-related myeloid neoplasms (tMN); the benefit of CT in eBC pts is often limited. Little is known about the prevalence and dynamics of CHIP in eBC pts. Methods: We prospectively identified two cohorts of pts with eBC: cohort A – pts receiving (neo)adjuvant CT with or without adjuvant endocrine therapy (ET); cohort B – pts receiving ET only. Blood was collected prior to initiation of treatment (T1) and after either (neo)adjuvant CT or 6-18 months of adjuvant ET (T2). We performed targeted sequencing of cryopreserved peripheral blood mononuclear cell (PBMC)-derived genomic DNA and defined CHIP as the presence of ≥1 pathogenic somatic mutation at variant allele fraction (VAF) ≥0.02. In additional analyses we used VAF≥0.005. Results: We enrolled 118 and 116 pts in cohorts A and B, respectively. Pts in cohort A were younger (median age 51 vs 57, p< 0.001), less frequently Caucasian (83.9 vs 96.6%; p=0.005) and former/current smokers (28.0 vs 43.1%, p=0.038). All pts in cohort B had hormone receptor-positive (HR+) eBC; in cohort A 50% of pts had HR+/HER2-, 16% had HR+/HER2+, 8.5% had HR-/HER2+ and 25.4% had HR-/HER2- eBC (p< 0.001). Pts in cohort A had higher stage (stage II-III 68.7 vs 27.6%; p< 0.001) and grade (grade 3 65.3 vs 15.5%; p< 0.001) tumors. Genetic testing was more frequently performed in pts receiving CT (88.1 vs 68.1%, p< 0.001), though the rate of germline pathogenic variants was similar (13.5 vs 17.7%, p=0.079). In cohort A, 38% received anthracyclines, 7% platinum and 57% anthracycline/platinum-sparing CT. Median time between T1 and T2 was 189.5 (150,406) and 280 (147, 425) days in cohort A and B (p< 0.001). The prevalence of CHIP, defined by mutations at VAF ≥ 0.02, was similar at T1 in cohort A (14.4%) vs B (18.1%) (p=0.556). Number of pts with new CHIP variants at T2 was also similar (A 3.4% vs B 6.0%) (p=0.373). After adjusting for age and stage, odds ratio (OR) of developing new CHIP variants in cohort B vs A was 1.28 (95% CI 0.32 – 5.68, p=0.733). Age correlated with baseline prevalence of CHIP (p< 0.001). Most frequent new CHIP variants at T2 in cohort A were DNMT3A (3), PPM1D (1), NF1 (1). To investigate whether pts receiving CT were more likely to have emergence of small hematopoietic clones, we assessed pathogenic variants present at VAF ≥0.005. These were detected at T1 in 55 (46.6%) and 61 (52.6%) pts in cohort A and B, respectively. Few pts without pathogenic variants at T1 developed them at T2 (3 pts in cohort A and 4 in cohort B). 21 pts (27 variants) in cohort A and 11 pts (12 variants) in cohort B had new variants at T2. Pts with new variants vs not (32 vs 202 pts) had similar characteristics, excepting age (median 60.5 vs 54.0, p=0.011). After correcting for age and stage, OR of developing new pathogenic variants given ET vs CT was 0.25 (95% CI 0.10-0.62, p=0.003). Most frequent newly detected variants were in DNMT3A (14), PPM1D (5), TET2 (4) and TP53 (2) in cohort A; DNMT3A (3), TET2 (3) and ZNF318 (2) in cohort B. Conclusions: In the CIRCE-eBC study, CT administration did not lead to emergence of CHIP over a 6-9 month period vs ET alone. This finding is reassuring in the setting of long life-expectancy for eBC pts and the association of CHIP with significant morbidity and mortality. However, consistent with known risk of development of MN, CT was associated with emergence of low frequency pathogenic variants in PPM1D and TP53, which have been associated with elevated risk of tMN. The evolution and prognostic role of these small clones is unclear and warrants additional investigation. Citation Format: Stefania Morganti, Qingchun Jin, Katheryn Santos, Christopher Gibson, Ashka Patel, Alex Wilson, Margaret Merrill, Julie Vincuilla, Samantha Stokes, Marla Lipsyc-Sharf, Tonia Parker, Tari King, Elizabeth A. Mittendorf, Giuseppe Curigliano, Melissa E. Hughes, Nabihah Tayob, Nancy U. Lin, Peter Miller, Sara Tolaney, Judy Garber, Heather A. Parsons. Clonal hematopoiesis of indeterminate potential after (neo)adjuvant chemotherapy versus endocrine therapy for early breast cancer: the CIRCE-eBC prospective cohort study [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 P5-14-03.

BACKGROUND: Abnormalities of the PI3kinase/AKT/mTOR signaling network are common in breast cancer (BC) and are associated with endocrine resistance. Everolimus, an mTOR-inhibitor increased PFS when combined with endocrine therapy (ET) in the metastatic setting and is thought to revert endocrine resistance. S1207 is a phase III randomized, placebo-controlled trial evaluating the role of everolimus in combination with ET in the adjuvant setting among patients with high-risk hormone receptor-positive, HER2-negative BC (NCT01674140). METHODS: Eligible patients were >18 years of age with histologically confirmed invasive hormone receptor-positive and HER2-negative high-risk BC. Four risk groups were defined as: 1) > 2cm node-negative disease (or pN1mi), and either an Oncotype DX® Recurrence Score (RS) > 25 or MammaPrint® high-risk category (MP high); 2) 1-3 positive nodes and either RS >25, MP high or a pathological grade 3 tumor; 3) >4 positive lymph nodes. Patients treated with neoadjuvant chemotherapy were eligible if: 4) after surgery had >1 lymph node involvement. Patients were randomized 1:1 to physician’s choice adjuvant ET in combination with one year of everolimus (10 mg PO daily) or ET plus placebo stratified by risk group. The primary endpoint was invasive disease-free survival (IDFS) evaluated by a stratified log-rank test. Secondary endpoints included overall survival (OS) and safety. The hazard ratio (HR) for treatment efficacy was estimated using Cox regression with stratification by risk groups. Subset analyses included preplanned evaluation within risk group and exploratory analyses of menopausal status and age. RESULTS: 1,939 patients were randomized between September 2013 and May 2019, of them 1,792 were eligible and included in the analysis (896 per arm). Primary reason for ineligibility was timing after chemotherapy/radiation or not high risk. Median age was 54 years (22-85) and 32% were premenopausal. With a median follow-up of 50.5 months, there were 389 IDFS events as of May 2022 (data cutoff). 5-year IDFS was 74.8% among patients treated with everolimus and 73.9% among patients treated with placebo, HR=0.93 (95% CI 0.76-1.14). However, the proportional hazards assumption was violated (p=0.02) suggesting differential treatment effect over time. The HR during the one year of treatment was 0.72 (95% CI 0.47-1.10) while after one year it was 1.00 (95% CI 0.80-1.26). The 5-year OS was 87.6% in the everolimus arm and 85.5% in the placebo arm, HR=0.98 (95% CI 0.75-1.28). Analysis by risk group did not show higher everolimus benefit as risk increased. No difference in IDFS or OS was seen among postmenopausal patients (IDFS HR=1.08 [95% CI 0.85-1.36], OS HR=1.19 [95% CI 0.87-1.61]). Among premenopausal patients, everolimus was associated with improved IDFS (HR=0.63 [95% CI 0.43-0.93]) and OS (HR=0.48 [95% CI 0.26-0.88]). Treatment completion of randomized therapy was lower in the everolimus arm compared to placebo (47.9% v 72.7%). Grade 3 and 4 toxicities were noted in 6.5% and 0.5% of patients in the placebo arm and in 31.2% and 3.7% in the everolimus arm respectively. CONCLUSIONS: Addition of one year of adjuvant everolimus to standard adjuvant ET did not improve IDFS or OS and was associated with low completion rate and increased AEs. Among premenopausal patients there was a benefit in IDFS and OS that is hypothesis generating. Future translational studies will evaluate potential predictors of everolimus benefit and drug toxicity. Citation Format: Marianna Chavez, Jieling Miao, Lajos Pusztai, Matthew P. Goetz, Priya Rastogi, Patricia A. Ganz, Eleftherios (Terry) Mamounas, Soonmyung Paik, Hanna Bandos, Wajeeha Razaq, Anne O’Dea, Virginia Kaklamani, Andrea L.M. Silber, Lisa E. Flaum, Eleni Andreopolu, Joseph Baar, Albert G. Wendt, Jennifer F. Carney, Priyanka Sharma, Julie R. Gralow, Danika L. Lew, William E. Barlow, Gabriel N. Hortobagyi. Results from a phase III randomized, placebo-controlled clinical trial evaluating adjuvant endocrine therapy +/- 1 year of everolimus in patients with high-risk hormone receptor-positive, HER2-negative breast cancer: SWOG S1207 [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 GS1-07.

Purpose/Objectives: Since the COVID-19 pandemic, telemedicine has become an attractive alternative to office visits in routine radiation oncology practice. The purpose of this study was to identify factors associated with patient preference for an initial consult telemedicine visit and correlation with clinical trial enrollment. Materials/Methods: We evaluated breast cancer patients seen during the open enrollment of a prospective randomized controlled non inferiority trial evaluating radiation fibrosis with five versus three fractions from 07/13/2020 to 05/13/2021. Univariate and multivariate logistic regression models were used to identify factors associated with virtual vs in-person initial consultation and enrolled vs not enrolled patients. All statistical tests were two-sided and the null hypothesis was rejected for p< 0.05. Results: We identified 476 patient consultations with 259 office visits and 217 telemedicine visits. On multivariate analysis, increased age, unemployment, chemotherapy receipt and radiation at NYU were associated with decreased usage of telemedicine for consultation visit. Out of 217 patients who underwent a telemedicine initial consultation, 10% were eligible to enroll on the trial and of those eligible, 76% enrolled. Out of 259 patients who underwent office visit initial consultation, 14% were eligible to enroll on the trial and of those eligible, 53% enrolled. Among eligible patients, there was no statistically significant difference in clinical trial enrollment between telemedicine and office visits. There was no statistically significant difference in patient characteristics between enrolled vs not enrolled patients. Conclusion: Though patient and disease characteristics remained similar between patients undergoing telemedicine and office visits consultations, increased age, unemployment and receipt of chemotherapy were associated with lower usage of telemedicine. Those who underwent in person initial consultation were also more likely to subsequently receive their radiation at our clinic. Further studies are needed to better define underlying reasons for patient selection and impact on care and trial enrollment in order to ensure equal access and benefit from telemedicine, especially in already vulnerable patient populations. Citation Format: Camille Hardy Abeloos, Julie Xiao, Cheongeun Oh, Olivier Maisonet, Naamit Gerber. Disparities in the uptake of telemedicine and implications for clinical trial enrollment in breast cancer patients [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 P4-07-11.

Glycobiology has proved to be a new frontier in oncology research in recent years. One sector of glycobiology involves examining glycan expression of cancerous cells. Glycans are complex carbohydrates found on cell surfaces, and patterns of aberrant glycan expression, such as increased sialylation and fucosylation, have been proposed as potential novel biomarkers of cancer tumorigenesis and metastasis. However, to our knowledge, there is little literature examining the differences in expression of high mannose glycans, a subtype of N-linked glycans, which is the focus of this study. Thirty-nine samples of malignant and surrounding benign tissue from breast cancer patients were collected from the Prisma Health Cancer Institute Biorepository. Additionally, forty malignant serum samples were collected—ten of these samples were from the same patients included in the tissue samples. Serum samples from ten healthy volunteers were also obtained as controls. The malignant samples included specimens from breast cancer staged I through IV at the time of the patients’ diagnosis. Samples were analyzed using MALDI-TOF mass spectroscopy for the presence of glycans by Emory Glycomics and Molecular Interactions Core. The known masses of sixty-one unique glycans were then compared to the spectra of the samples analyzed to determine the type of glycans present, and the relative amount of each glycan present was determined using the area under the curve in the spectral data. Data analysis revealed the means of the area under the curve for high mannose glycans in the malignant and normal tissue samples to be 247.18 and 163.6 respectively; the t-test established the difference in these means to be statistically significant (p-value, 0.0138). This finding was consistent in serum samples; the mean area under the curve for malignant and normal serum was 1650.34 and 376.26 respectively (p-value, >.0001). Furthermore, there were differences in expression of high mannose glycans between stages of breast cancer, with expression in stage III being significantly greater than expression in stage II in both serum (p-value, .0097) and tissue (p-value, .0003) samples. The results of this analysis suggest a higher expression of high mannose glycans to be a promising biomarker for breast cancer. This could lead to important clinical applications such as being a helpful distinction in obtaining negative margins during tumor resection, as well as providing a non-invasive diagnostic method. Future research could include expanding the sample size and comparing the glycan composition of the samples to a library specific for high-mannose type glycans, with the goal of establishing a signature high-mannose expression pattern in each stage of cancer. Citation Format: Alex Kesic, Avery Funkhouser, Jonah Shealy, Julie Martin, W. Larry Gluck, William J. Edenfield, Anna Blenda. Elevated Expression of High Mannose Glycans in Tissue and Serum Samples of Breast Cancer Patients [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 P2-26-22.

Effective treatments for de novo and treatment-emergent small-cell/neuroendocrine (t-SCNC) prostate cancer represent an unmet need for this disease. Using metastatic biopsies from patients with advanced cancer, we demonstrate that delta-like ligand 3 (DLL3) is expressed in de novo and t-SCNC and is associated with reduced survival. We develop a PET agent, [89Zr]-DFO-DLL3-scFv, that detects DLL3 levels in mouse SCNC models. In multiple patient-derived xenograft models, AMG 757 (tarlatamab), a half-life–extended bispecific T-cell engager (BiTE) immunotherapy that redirects CD3-positive T cells to kill DLL3-expressing cells, exhibited potent and durable antitumor activity. Late relapsing tumors after AMG 757 treatment exhibited lower DLL3 levels, suggesting antigen loss as a resistance mechanism, particularly in tumors with heterogeneous DLL3 expression. These findings have been translated into an ongoing clinical trial of AMG 757 in de novo and t-SCNC, with a confirmed objective partial response in a patient with histologically confirmed SCNC. Overall, these results identify DLL3 as a therapeutic target in SCNC and demonstrate that DLL3-targeted BiTE immunotherapy has significant antitumor activity in this aggressive prostate cancer subtype. Significance: The preclinical and clinical evaluation of DLL3-directed immunotherapy, AMG 757, and development of a PET radiotracer for noninvasive DLL3 detection demonstrate the potential of targeting DLL3 in SCNC prostate cancer.

We recently derived an absolute breast cancer risk prediction model, the Black Women’s Health Study (BWHS) model, for breast cancer in U.S. Black women using data from three large case-control studies and validated it in independent prospective data from the Black Women’s Health Study (Palmer 2021). The BWHS model includes epidemiologic risk factors as well as family history of breast cancer and family history of prostate cancer. It does not include genetic variants because at the time of model development breast cancer polygenic risk scores performed poorly in women of predominantly African ancestry, primarily due to differences in allele frequency and linkage disequilibrium. More recently, Gao et al. (2022) developed and tested a polygenic risk score (PRS) using 56,943 SNPs for breast cancer in women of African ancestry (AA) based on 9,235 breast cancer cases and 10,184 controls from a large pooled analysis of studies from African American and African women; the c-statistic from cross-validation was 0.581, considerably better than in previous efforts. We evaluated whether adding this AA-PRS to the BWHS risk prediction model would improve risk stratification. We conducted a nested case-control study of 901 breast cancer cases and 1,576 controls matched on age and most recent questionnaire completed from among BWHS participants for whom genome-wide association data were available and who had not been included in the collaboration from which the PRS was derived and tested. We examined discriminatory accuracy, estimated by the area under the receiver operating characteristic curve (AUC), for the risk prediction model alone, the PRS alone, and the combination of risk prediction model and PRS, controlling for the matching factor “questionnaire cycle”. We conducted the analyses within strata of 5-year age and then combined results using inverse-variance weighting. In preliminary analyses, the AUC was 0.579 for the risk prediction model alone and 0.600 for the AA-PRS alone. When the AA-PRS and the BWHS risk prediction model were both used as predictors in a logistic regression model, the AUC increased from 0.579 to 0.622. This improvement in risk stratification is similar to what Kachuri et al. (2020) obtained in an analysis of U.K. Biobank data, where adding a PRS to epidemiologic and personal risk factors showed an improvement from 0.572 to 0.635 in women of European ancestry. The present study provides external validation of a recently derived AA PRS and demonstrates the potential for improving risk stratification for U.S. Black women by adding a PRS to a breast cancer risk prediction model that already includes family history of breast cancer. Citation Format: Gary R. Zirpoli, Kathryn L. Lunetta, Ruth M. Pfeiffer, Julie R. Palmer. PD14-06 Polygenic risk score added to risk calculator improves prediction of breast cancer in U.S. Black women [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 PD14-06.

Background: Prognostic and predictive tools are needed to optimize treatment for women diagnosed with ductal carcinoma in situ (DCIS). While radiotherapy (RT) is standard of care for DCIS after breast conserving surgery (BCS), those at low-risk for ipsilateral breast recurrence (IBR) risk may be treated without RT. Low-risk has been defined as the absence of high risk clinicopathologic (CP) factors, including larger (>2 cm), palpable, or high nuclear grade (NG) tumors, and younger age (< 50 yrs). However, prospective trials have failed to identify low risk patients (pts) who do not clinically benefit from RT after BCS (RTOG 9804). DCISionRT® (PreludeDxTM, CA) is a 7-gene predictive biosignature providing a validated score (DS) to assess the 10-yr IBR risk and RT benefit, using individual tumor biology and CP factors. This study assessed total 10-yr IBR rates, RT benefit, and number needed to treat (NNT) for risk groups defined by biosignature and CP criteria. Methods: DCIS patients (n=926) from four international cohorts (median follow up 8.5 yrs, 1-3rd quartile 5.8 – 10.2 yrs) treated with BCS (negative margins), with (n=641) and without RT (n=335), had formalin-fixed paraffin-embedded tissues analyzed at a CLIA lab (PreludeDx, Laguna Hills, CA) for DCISionRT with a Residual Risk subtype (RRt). A biosignature Low Risk group (DS≤2.8 without RRt) was contrasted to a High Risk group comprising Elevated Risk (DS>2.8 without RRt) and Residual Risk (DS>2.8 with RRt) groups. Low-risk CP groups were RTOG 9804-like (NG1-2, non-palpable, negative margins, screening detected) or (age >50 and NG 1-2). Total 10-yr IBR rates were evaluated using Cox Proportional Hazards and Kaplan Meier analysis by treatment, biosignature and CP risk groups. NNT was determined with 10-yr IBR rate differences with RT. Results: The biosignature classified 37% (n=338) of women as Low Risk and 63% (n=588) as High Risk. Among women who did not receive RT, biosignature Low Risk pts had lower IBR than biosignature High Risk pts (5.6% vs. 25.7%, p Conclusion: In a large multicenter population, DCISionRT was a better predictor of 10-yr prognosis and RT benefit than CP criteria alone. Pts with biosignature Low Risk disease, comprising about 1/3 of CP high-risk pts, had no significant RT benefit. Whereas pts with biosignature High Risk disease, comprising about 1/2 of CP low-risk pts, significantly benefited from RT, highlighting the lack of accuracy of these CP factors in assessing RT benefit. Table 1. Ten-Year Risk of Ipsilateral Breast Recurrence (IBR) Citation Format: Rachel Rabinovitch, Frank Vicini, Chirag Shah, Julie A. Margenthaler, Brian J. Czerniecki, Pat Whitworth, DAVID J. DABBS, G Bruce Mann, Fredrik Wärnberg, Sheila Weinmann, Michael Leo, Jess Savala, Steven C. Shivers, Karuna Mittal, Troy Bremer. PD15-07 7-gene predictive biosignature improves risk stratification for breast ductal carcinoma in situ patients compared to clinicopathologic criteria, identifying a low risk group not clinically benefiting from adjuvant radiotherapy [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 PD15-07.

Obesity induces numerous physiological changes that can impact cancer risk and patient response to therapy. Obese patients with cervical cancer have been reported to have superior outcomes following chemoradiotherapy, suggesting that free fatty acids (FFA) might enhance response to radiotherapy. Here, using preclinical models, we show that monounsaturated and diunsaturated FFAs (uFFA) radiosensitize cervical cancer through a novel p53-dependent mechanism. UFFAs signaled through PPARγ and p53 to promote lipid uptake, storage, and metabolism after radiotherapy. Stable isotope labeling confirmed that cervical cancer cells increase both catabolic and anabolic oleate metabolism in response to radiotherapy, with associated increases in dependence on mitochondrial fatty acid oxidation for survival. In vivo, supplementation with exogenous oleate suppressed tumor growth in xenografts after radiotherapy, an effect that could be partially mimicked in tumors from high fat diet–induced obese mice. These results suggest that supplementation with uFFAs may improve tumor responses to radiotherapy, particularly in p53 wild-type tumors. Significance: Metabolism of monounsaturated and diunsaturated fatty acids improves the efficacy of radiotherapy in cancer through modulation of p53 activity. See related commentary by Jungles and Green, p. 4513