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563 Background: A polygenic risk score (PRS) consisting of 313 single nucleotide polymorphisms (PRS313) is associated with risk of breast cancer and contralateral breast cancer. One of the most promising clinical applications for the use of PRS is to provide a personalized risk assessment to individualize breast cancer screening programs. This study aimed to evaluate the association of the PRS313 with clinical-pathological characteristics and survival of breast cancer. Methods: Women of European ancestry with invasive breast cancer were included, 98,397 women from the Breast Cancer Association Consortium (BCAC) and 683 women from the MINDACT trial. Associations between PRS313 (continuous, per SD) and clinical-pathological characteristics, including the 70-gene signature for patients included in MINDACT, were evaluated with logistic regression analyses. Associations of PRS313 with overall survival (OS), breast cancer-specific survival (BCSS) and distant metastasis-free interval (DMFI) were evaluated with Cox regression analyses, adjusted for clinical-pathological characteristics and treatment. Results: The PRS313 was associated with favorable tumor characteristics. In BCAC, increasing PRS313 was mostly associated with lower grade, hormone receptor-positive tumors, and with smaller tumor size. In MINDACT, PRS313 was associated with a low risk 70-gene signature, but the association was attenuated after adjustment for clinical-pathological characteristics. In BCAC, univariable analyses showed an association of PRS313 with better survival, hazard ratio (HR) per unit SD increase of PRS313 for OS: 0.96 (95% confidence interval (CI): 0.94-0.97), for BCSS HR: 0.96 (95% CI: 0.94-0.98) and for DMFI HR: 0.98 (95% CI: 0.96-1.00). The association in the unadjusted analysis was explained by differences in clinical-pathological characteristics (and treatment) and disappeared after adjustment: OS HR: 1.01 (95% CI: 0.98-1.05), BCSS HR: 1.02 (95% CI: 0.98-1.07) and DMFI HR: 1.03 (95% CI: 0.99-1.07). Conclusions: An increased PRS313 is associated with favorable tumor characteristics but was not independently associated with prognosis. This information is crucial input for modelling effective stratified screening programs, especially in the current era of optimized (systemic) treatments. Given the significant increase in breast cancer risk associated with increasing PRS313, absolute breast cancer mortality will still be higher for women with higher PRS313.

587 Background: Residual cancer burden (RCB) is a continuous score that captures the amount of residual cancer after neoadjuvant chemotherapy and predicts disease recurrence and survival across all breast cancer subtypes. RCB score 0 corresponds to pathological complete response (pCR; ypT0, ypN0). We hypothesize that comparison of the distributions of RCB scores between randomized treatment arms of a trial could predict treatment effect on recurrence free survival better than comparison of pCR rates only. Methods: The cancer Treatment Efficacy Score (TES) compares efficacies of two treatments using non-continuous RCB results. We examined (i) area between cumulative distribution (ABC) functions; (ii) density ratio of RCB scores; and (iii) density difference of RCB scores from two treatments, to select the most efficient metric to compute TES. A random permutation procedure was used to estimate the p-value from each test. These methods were applied to data from the durvalumab/olaparib arm and corresponding controls of the I-SPY2 trial, separately by molecular subtype. In subsampling and simulation experiments we assessed robustness of results including power and false positive rate control under variable sample sizes to select the most robust TES metric. The other 11 experimental arms of I-SPY2 were used to assess the performance of the final metric. We calculated correlation between TES and (i) pCR rate difference, and 3- and 5-year (ii) event-free (EFS) and (iii) distant recurrence free survivals (DRFS). Results: RCB scores are multimodal and do not follow normal distribution.In simulated data ABC provided more stable results than the other methods, had good power, performed well with small sample sizes, resulted in low false positive rate, required the least computational time, and therfore was selected as the TES metric for validation in 11 arms of I-SPY2. We found a high correlation between difference in pCR rate and TES value across all molecular subtypes in each of the 11 trial arms (r = 0.92, p = 1.7e-8). There was also significant linear relationship between TES and survival estimates in EFS (r = 0.58, p = 9.3e-3 for 3-years survival; r = 0.62, p = 4.8e-3 for 5-years survival) and DRFS (r = 0.56, p = 1.2e-2 for 3-years survival; r = 0.54, p = 1.8e-2 for 5-years survival). Statistically significant TES score correlated significantly with higher benefit in 3-years survival (p = 9.7e-4 for EFS; p = 5.7e-3 for DRFS) and 5-years survival (p = 9.7e-4 for EFS; p = 3.0e-3 for DRFS). In most instances, this correlation with survival was higher than seen with pCR difference. Conclusions: TES is a novel more optimal metric to identify the more effective cytotoxic neoadjuvant regimen from the entire distribution of pathologic response that significantly correlates with event and recurrence free survival and may serve as a better surrogate than pCR rate difference.

500 Background: Gene signatures have proven successful in identifying patients with a low risk of distant recurrence who could forego chemotherapy (CT) and are currently included in international treatment guidelines for breast cancer. For the 70-gene signature (MammaPrint) an additional threshold was established within the low risk category to identify patients with an ultralow risk of distant recurrence. In independent cohorts, these patients had excellent breast cancer specific survival at 15 years, suggesting that ultralow risk cancers represent indolent disease (Esserman, JAMA Oncol 2017, Delahaye, BC Res Treat 2017). Here we evaluate survival of patients with an ultralow risk 70-gene signature who participated in the randomized phase 3 MINDACT trial (Piccart, Lancet Oncol 2021). Methods: Of the 6,693 patients enrolled in the MINDACT trial (EORTC 10041/BIG 3-04) between 2007-2011, profiling revealed an ultralow risk 70-gene signature in 1,000 patients (15%). We assessed 5- and 8-year distant metastasis free interval (DMFI) and breast cancer specific survival (BCSS) in patients stratified by 70-gene signature result (high, low, ultralow), and within the ultralow risk group stratified by clinical risk. For these exploratory analyses, we used Kaplan-Meier estimates for time to event endpoints and Cox-regression models to calculate hazard ratio’s (HR). Results: Median follow-up was 8.7 years. Among the ultralow risk patients (n = 1,000), 67% were ≥50 years, 81% had tumors < 2cm, 80% were lymph node negative, 96% had grade 1 or 2 tumors and 99% were ER-positive. Systemic therapy was received by 83% of patients (69% endocrine therapy (ET), 14% ET + CT) and 16% received no adjuvant systemic treatment (AST). Survival estimates for all endpoints are shown in the table; 8-year DMFI was 97.0% (95% CI 95.8-98.1) for ultralow risk. The 8-year DMFI in ultralow risk patients who received no AST or ET only was 97.8% (95% CI 95.3-100) and 97.4% (95% CI 96.1-98.7), respectively. The HR for DMFI was 0.66 (95% CI 0.46-0.95) for ultralow vs low risk, after adjusting for tumor and treatment characteristics (preliminary results). Conclusions: In this prospective study, patients with an ultralow risk 70-gene signature have an excellent prognosis with 8-year BCSS above 99% regardless of clinical risk status, and with an 8-year DMFI of 95-98%.[Table: see text]

502 Background: The 70-gene MammaPrint (MP) assay predicts risk of distant recurrence (DR) in hormone-receptor positive early-stage breast cancer and classifies cancers as Low Risk or High Risk. NSABP B-42 evaluated ELT in patients (pts) who had completed 5 yrs of adjuvant endocrine therapy (tx). The primary objective was to determine the utility of MP to identify pts enrolled in NSABP B-42 who are likely to benefit from ELT. Methods: A total of 1,866 pts from B-42 had available MP results. Primary endpoint is DR. Secondary endpoints are disease-free survival (DFS) and breast cancer-free interval (BCFI). For the primary analysis, pts were classified as High Risk (MP-H) (MP score ≤0.000) or Low Risk (MP-L) (MP score > 0.000). Exploratory analyses were performed for MP-L subcategories: MP Ultralow Risk (MP-UL) (MP score > 0.355) and MP-L but not MP-UL (MP-LNUL) (MP score > 0.000, ≤0.355). Likelihood ratio test based on stratified Cox proportional hazards (PH) model was used for treatment by risk group interaction. Stratified log-rank test was used to compare treatment groups. Hazard ratios and 95% CI were computed based on the stratified Cox PH model. Results: Among 1,866 pts, 706 (38%) were MP-H and 1,160 (62%) were MP-L. Of the MP-L, 252 (22%) were MP-UL. There were no significant differences in the distribution of patient and tumor characteristics between the MP group and the rest of the B-42 cohort, except for HER2 status. ELT effect was more pronounced in the MP cohort than in the overall B-42 population. For DR, there was statistically significant ELT benefit in MP-L (HR = 0.43, 95% CI 0.25-0.74, p = 0.002), but not MP-H (HR = 0.65, 0.34-1.24, p = 0.19) (interaction p = 0.38). For DFS, there was statistically significant ELT benefit in MP-L, but not MP-H (interaction p = 0.015). Similar findings were observed for BCFI (interaction p = 0.006). Within subcategories of MP-L, there was statistically significant ELT benefit in MP-LNUL, but not in MP-UL for all three endpoints, however the power in MP-UL was limited due to low number of pts (Table). Clinical trial information: 00382070. Conclusions: Statistically significant ELT benefit was observed for MP-L, but not MP-H. The treatment by risk group interaction was not statistically significant for DR, but it was for DFS and BCFI. The benefit appears to be stronger in MP-LNUL than in MP-UL. NCT: 00382070. Support: U10CA180868, -180822, U24CA196067; Novartis; Agendia.[Table: see text]

519 Background: About one third of patients with hormone-receptor-positive (HR+), HER2‐ primary breast cancer with residual invasive disease after neoadjuvant chemotherapy will relapse despite adjuvant endocrine therapy. Therapeutic inhibition of cyclin-dependent kinase 4 and 6 (CDK 4/6) by palbociclib combined with endocrine therapy demonstrated highly relevant efficacy in metastatic breast cancer. The phase III PENELOPE-B (NCT01864746) study did not show a significant benefit from palbociclib in women with centrally confirmed HR+, HER2- primary breast cancer without a pathological complete response after taxane‐containing neoadjuvant chemotherapy and at high-risk of relapse (CPS‐EG score ≥3 or 2 and ypN+) for the primary endpoint (Loibl et al. JCO 2021). Methods: After completion of neoadjuvant chemotherapy and locoregional therapy, PENELOPE-B patients were randomized (1:1) to receive 13 cycles (1 year) of palbociclib 125mg daily or placebo on days 1-21 in a 28d cycle in addition to standard endocrine therapy. Analysis of the primary endpoint of invasive disease-free survival (iDFS) was planned after 290 events. Secondary objective included iDFS in luminal-B group by treatment. Gene expression in post-neoadjuvant surgical residual tumor tissue samples was profiled using the HTG EdgeSeq Oncology Biomarker Panel targeting 2559 genes (HTG Molecular Diagnostics Inc.). Based on 91 genes of this panel the AIMS subtype (Paquet & Hallett, JNCI 2014) was calculated. Results: Gene expressions were measured in tumors from 906 of 1250 (72%) PENELOPE-B patients; 663 had LumA subtype, 64 LumB, 135 NormL, 16 BasalL, and 28 HER2E. Compared to LumA the LumB patients were older, had higher post-neoadjuvant Ki-67, higher risk status (CPS-EG), and higher grade; no significant correlation was found for the region of participating sites, cT, ypT, and ypN. Patients with LumB tumors had an estimated 3-year iDFS of 71.9% with palbociclib vs 44.8% with placebo HR = 0.50 (0.24-1.05); outcome was similar in patients with LumA tumors (3-year iDFS 83.9% vs 79.5%, HR = 0.93 (0.68-1.28), interaction p = 0.132); this was confirmed in multivariable analyses. Ki-67 by IHC and proliferation biomarkers from the HTG panel also showed no significant interaction with treatment. Conclusions: PENELOPE-B did not show a benefit from the addition of 1 year palbociclib to endocrine therapy compared to placebo in the total enrolled high-risk primary breast cancer population. However, the small group of luminal-B tumors (n = 64) derived benefit from palbociclib, although without a statistically significant interaction. Further investigation is required in a larger cohort to validate a palbociclib benefit that might be confined to this group.

506 Background: The 70-gene signature MammaPrint has been shown to identify breast cancer patients for whom adjuvant chemotherapy (CT) could be safely omitted even in the presence of unfavorable standard clinical-pathological criteria. The MINDACT primary endpoint at 5 years median follow-up was met in 2016 (Cardoso et al, NEJM 2016) with a distant metastasis free survival (DMFS) rate at 5 years of 94.7% (95% CI: 92.5-96.2) in clinical high (C-High) / genomic low (G-Low) risk patients who received no CT. Longer follow-up is now available. Methods: 6693 patients were enrolled in the prospective phase III randomized MINDACT study (EORTC 10041/BIG3-04) between 2007-2011. We assessed the DMFS rate at 5 years in the primary test (PT) population of C-High / G-Low patients who were randomized to receive no CT (n = 644). As secondary analysis, we evaluated DMFS and overall survival (OS) in the intention to treat (ITT) population of the C-High / G-Low group randomized to CT vs no CT (n = 749 and 748 respectively). Comparisons between CT and no CT groups are low-powered. We used Kaplan-Meier estimates for time to event endpoints and hazard ratios (HR) with 95% CI from cox-regression models adjusted for stratification factors used for the randomization. Results: The median follow-up is 8.7 years, resulting in an updated 5-year DMFS rate for the PT population of C-High / G-Low patients with no CT of 95.1% (95% CI 93.1-96.6). The updated outcomes of the ITT population of C-High / G-Low patients are shown in the table. Further analyses will update the suggested age-dependent effect of CT omission for luminal breast cancer seen at 5 years in pre- versus post-menopausal women as in Tailor-X (Piccart et al, SABCS 2019). Conclusions: The primary DMFS endpoint at 5 years continues to be met in CT untreated C-High / G-Low risk women, confirming MINDACT as a positive de-escalation study. With longer follow-up and in line with the natural history of luminal breast cancer, more distant relapses do occur but the estimated gain of 2.6% for CT administration in C-High / G-Low patients remains small in light of CT harmful effects. The level IA evidence for the clinical utility of the 70-gene signature for adjuvant CT decision making is maintained. Clinical trial information: NCT00433589 . [Table: see text]

e23171 Background: NCI PROMIS assesses physical, mental and social health across multiple health conditions. Despite interest in using PROMIS in oncology trials and clinical care, reference values in cancer are not well established. Methods: Electronic intake questionnaires assessing self-reported history and 8 PROMIS domains (depression, anxiety, fatigue, sleep-related impairment (SRI), sleep disturbance, cognitive function, applied cognition and physical function) are sent to all new patients (pts). 2886 pts with self-reported breast cancer completed the questionnaire/consented to research. PROMIS T-Scores were calculated using the Health Measures system. Results: For all domains except depression, cognitive function and applied cognition, pts had clinically meaningful ( > 3 point diff.) worse mean PROMIS scores than US means (50). Compared to stage 0-III, stage IV pts had worse scores for all assessed domains (p < 0.05). Among Stage IV pts < 49, QoL was significantly worse in 7/8 domains (see table). Across all age groups, there were significant differences in mean PROMIS scores for Stage IV pts in anxiety, depression, cognitive function and applied cognition (p < 0.05). Conclusions: PROMIS scores among pts indicate impaired QoL in multiple domains. These scores provide insight into the physical, mental and social health of our pts and can serve as robust estimates for breast cancer trials and clinical care. [Table: see text]

2631 Background: Response to immune checkpoint inhibitors has been associated with immune activation and mutational load within a tumor. Previous results in other tumors have implicated MHC II protein tumor cell expression as a response predictor to immune checkpoint inhibitors. In the I-SPY 2 TRIAL, the anti-PD1 therapeutic antibody pembrolizumab (P) was available to HER2-negative subtypes and graduated in both the HR+/HER2- and TNBC signatures. Pre-specified biomarker analysis was performed to test tumor MHC II expression as a predictor of response to P in the I-SPY 2 TRIAL based on its central role in tumor antigen presentation. Methods: 156 patients (P: 67, controls: 89) had RPPA and pCR data. RPPA-based quantitative data for pan-MHC II protein isotypes HLA-DR/DP/DQ/DX and HLA-DR protein isotype was obtained from LCM-enriched tumor epithelium, and protein levels were assessed for association with pCR in the P and control arms separately using the Wilcoxon Rank Sum test (p < 0.05). Analysis was also performed in the HR+ and HR- subgroups. Markers were analyzed individually; p-values are descriptive and were not corrected for multiple comparisons. Results: Across all P- treated patients, the HLA class II molecules –DR and -DR/DP/DQ/DX had a positive association with response to P (p = 0.014 and p = 0.001). Expression of HLA-DR/DP/DQ/DX also had a positive association with response to P in HR+ tumors. Neither of these associations were seen in the control arm samples. Conclusions: The observation of elevation of MHC II protein expression in HER2- responding patients treated with P suggests that activation of antigen peptide exchange facilitated by these molecules in T and B cells may enhance response to P treatment.

1506Background: The Breast Cancer Surveillance Consortium (BCSC) Risk Calculator is a validated and widely used risk model that predicts five- and ten-year risk of developing invasive breast cancer...

12099Background: In the I-SPY 2 TRIAL, the allosteric AKT inhibitor MK2206 was available to all HR/HER2 subtypes and graduated in the HR-/HER2+ signature. Qualifying biomarker analysis was performe...

541Background: Breast cancer patients with estrogen receptor (ER)-positive disease have a continuous long-term risk for fatal breast cancer spanning more than 20 years, but the biological factors i...

12103Background: Trebananib (T), an angiopoietin 1/2 neutralizing peptibody that inhibits interaction with TIE2 receptors, was available to all HR/HER2 subtypes in the I-SPY2 TRIAL. The agent did n...

Purpose Bilateral prophylactic oophorectomy (BPO) is widely used for cancer risk reduction in women with BRCA1/2 mutations. Many premenopausal women choose to take hormone replacement therapy (HRT) after undergoing BPO to abrogate immediate symptoms of surgically-induced menopause. Thus, we evaluated whether the breast cancer risk reduction conferred by BPO in BRCA1/2 mutation carriers is altered by use of post-BPO HRT. Methods We identified a prospective cohort of 462 women with disease-associated germline BRCA1/2 mutations at 13 medical centers to evaluate breast cancer risk after BPO with and without HRT. We determined the incidence of breast cancer in 155 women who had undergone BPO and in 307 women who had not undergone BPO on whom we had complete information on HRT use. Postoperative follow-up was 3.6 years. Results Consistent with previous reports, BPO was significantly associated with breast cancer risk reduction overall (hazard ratio [HR] = 0.40; 95%CI, 0.18 to 0.92). Using mutation carriers without BPO or HRT as the referent group, HRT of any type after BPO did not significantly alter the reduction in breast cancer risk associated with BPO (HR = 0.37; 95% CI, 0.14 to 0.96). Conclusion Short-term HRT use does not negate the protective effect of BPO on subsequent breast cancer risk in BRCA1/2 mutation carriers.

524 Background: A key node of growth and survival signaling pathways is the Akt serine/threonine kinase that activates mTOR and downstream effectors. I-SPY 2 is a randomized neoadjuvant trial to te...

10597 Background: Classification of breast cancers into molecular subtypes may be important for the proper selection of therapy for patients with early breast cancer. Previous analyses had shown that breast cancer subtypes have distinct clinical outcome (Sorlie, PNAS, 2001; Esserman, BCRT, 2011). Herein, we analyze using MammaPrint together with an 80-gene molecular subtyping profile (BluePrint) the response to neo-adjuvant chemotherapy and long term outcomes. Methods: This study was carried out on data from 144 patients from the I-SPY I trial; 232 patients from biomarker discovery program at MD Anderson (133 and 99 respectively; Hess, 2006, JCO; Iwamoto, 2011, BCRT); and 68 patients from City of Hope (Somlo, ASCO, 2010). All patients were treated in the neo-adjuvant setting with standard chemotherapy. MammaPrint and BluePrint were determined on 44K Agilent arrays run at Agendia or available through the I-SPY 1 data portal, or from Affymetrix U133A arrays. MammaPrint and BluePrint resulted in 4 distinct molecular groups: Luminal A (MammaPrint Low-risk/Luminal-type), Luminal B (MammaPrint High-risk/Luminal-type), Basal-type and HER2-type. Results: The overall pCR of this patient cohort was 22% but differed substantially among the subgroups. pCR was observed in 5% of the Luminal-A samples and 10% of Luminal-B, in 39% of the HER2-type samples and in 33% of the Basal-type samples. Patients with Basal-type tumors had a 5-year DFS of 71%; HER2-type had a 5-year DFS of 67%(n=71); 69% in HER2-type subgroup not treated with HER2-targeted therapy (n=45); Luminal-B type had a 5-year DFS of 77% and Luminal-A type showed 5-year DFS of 95%. Conclusions: We observed marked differences in response and DFS to neo-adjuvant treatment in groups stratified by MammaPrint and BluePrint. These findings confirm differences in chemotherapy response among molecular subgroups and indicate that the BluePrint and MP profile used for this analysis helps to further establish a clinical correlation between molecular subtyping and treatment outcomes.