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575 Background: Given improvements in systemic therapy, pathologic complete response (pCR) rates following neoadjuvant chemotherapy were over 60% in breast cancer patients in recent clinical trials, especially in human epidermal growth factor receptor 2 (HER2)-positive and triple negative cases. While racial minority groups were associated with worse survival outcomes despite receiving standard of care in prospective studies, they were under-represented in clinical trials. To address this knowledge gap, we performed an observational cohort study to evaluate pCR and survival outcomes stratified by racial and ethnic groups. Methods: The National Cancer Database (NCDB) was queried for female patients with stage I-III breast cancer diagnosed between 2010 and 2017 treated with neoadjuvant chemotherapy followed by surgery. Cochran-Armitage test was used to analyze the trend of pCR over time. Logistic multivariable analysis (MVA) was used to identify variables associated with pCR defined as ypT0/isN0. Cox MVA was used to analyze the overall survival (OS) benefit. Results: A total of 105,804 patients (n = 72,631 for non-Hispanic white [NHW], n = 7,632 for Hispanic white [HW], n = 19,505 for black, n = 4,393 for Asian or Pacific Islander [API], n = 1,643 for other race) were included for analysis. Median follow up was 49.2 months (interquartile range 32.7-71.3). Overall pCR rate increased from 15.1% in 2010 to 27.2% in 2017, largely driven by API women (15.7% to 31.6%) and hormone receptor (HR)-HER2+ tumors (28.6% to 53.1%; all trend p < 0.001). On logistic MVA, when compared to NHW women, HW women were more likely to have pCR for HR-HER2+ (adjusted odds ratio [aOR] 1.18, p = 0.02) and HR+HER2+ tumors (aOR 1.29, p = 0.005), while black women were more likely to have pCR for HR+HER2- tumors (aOR 1.13, p = 0.01) and less likely for HR-HER2+ (aOR 0.80, p < 0.001) and triple negative tumors (aOR 0.82, p < 0.001). API women were more likely to have pCR for HR-HER2+ tumors compared to NHW women (aOR 1.17, p = 0.04). On Cox MVA, when compared to NHW women, HW (ypT+N0: adjusted hazards ratio [aHR] 0.75, p < 0.001; ypN+: aHR 0.79, p < 0.001) and API women (ypT0/isN0: aHR 0.52, p = 0.005; ypT+N0: aHR 0.63, p < 0.001; ypN+: aHR 0.86, p = 0.03) were associated with improved OS, while black women were associated with worse OS for ypN+ only (aHR 1.18, p < 0.001). Conclusions: To our knowledge, this is the largest study using a nationwide oncology database suggesting the improving trend of pCR rate over time for all racial cohorts. In our study, when compared to NHW, HW and API women were more likely to have pCR for select HER2+ tumors, while black women were less likely to have pCR for HR-HER2+ and triple negative tumors but not for HR+HER2- tumors. HW and API women were associated with improved survival in the setting of any residual disease compared to NHW women, while black women were associated with worse survival only for residual nodal disease.

576 Background: Among patients with hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer, several prospective studies investigated various gene expression assays, such as 21-gene recurrence score (21 RS) and 70-gene signature (70 GS), to identify a subgroup of patients with pathologic complete response (pCR) from neoadjuvant chemotherapy. However, in the absence of large prospective trials to validate such findings, the National Comprehensive Cancer Network guideline does not recommend the routine adoption of such assays in the setting of neoadjuvant therapies. To address this knowledge gap, we performed an observational cohort study to compare pCR and survival outcomes based on these assays. Methods: The National Cancer Database (NCDB) was queried for female patients diagnosed between 2010 and 2017 with stage I-III breast cancer who underwent neoadjuvant chemotherapy and either 70 GS or 21 RS. Logistic multivariable analysis (MVA) was performed to identify variables associated with pCR. Cox MVA was performed to evaluate overall survival (OS). Subgroup analyses were performed among patients with favorable hormone receptor status (hormone receptor-positive, HER2-negative) and with RS ≥26 instead of RS ≥31. Results: A total of 3,009 patients met our inclusion criteria, with 2,075 (n = 1,287 for RS < 31, n = 788 for RS ≥31) and 934 (n = 175 for low risk, n = 759 for high risk) patients who underwent 21 RS and 70 GS, respectively. The median follow up was 48.0 months (interquartile range 32.2-66.7). On logistic MVA for all patients, those with a high risk from 70 GS or with RS ≥31 were more likely to have pCR. When compared to RS ≥31, a high risk from 70 GS was not associated with pCR. However, among those with favorable hormone receptor status, similar findings were noted, except that those with a high risk group from 70 GS were less likely to have pCR compared to those with RS ≥31. On Cox MVA for all patients, pCR was associated with improved OS. While RS ≥31 was associated with worse mortality, a high risk from 70 GS was not. No interaction was observed between pCR and risk groups for OS in both groups (interaction p = 0.23 for 70 GS, p = 0.66 for 21 RS). When analyses were repeated using a high risk group from 21 RS defined as RS ≥26, similar findings were noted, except that having favorable hormone receptor status and RS ≥26 was not associated with pCR when compared to the high risk from 70 GS. Conclusions: To our knowledge, this is the largest study using a nationwide oncology database suggesting that high recurrence risk groups in both assays were associated with pCR and that pCR was associated with improved survival. For those with favorable hormone receptor status, RS ≥31 may be a more selective prognostic marker. Further studies would be warranted to investigate the role of gene expression assays in the setting of neoadjuvant chemotherapy.

e12113 Background: Neoadjuvant chemotherapy (NAC) is an important modality in breast cancer treatment. We sought to identify pre-treatment prognostic factors in patients who had positron emission tomography paired with diagnostic quality contrast-enhanced CT (PET/CT) prior to neoadjuvant chemotherapy with respect to pathologic complete response (pCR) , survival and relapse-free survival (RFS). Methods: We retrospectively analyzed 118 breast cancer patients who had pre-treatment PET/CT imaging and received NAC from 2008-2014. We collected data on molecular markers, PET/CT, pCR, survival, and disease status. Results: The median follow up was 44 months(range 7.3-101.5),median age was 51 years; 47% were stage II, 53% stage III. 52% of patients had hormone receptor (HR) positive/HER2 negative disease, 31% of tumors were HER2 positive, and 17% of tumors were triple-negative. 92.5% with HER2 positive tumors received NAC containing at least one HER2 targeted agent. Pre-treatment standard uptake value (SUV) max of the primary breast tumor showed no statistically significant relationship to survival, RFS, or pCR. PET avid (>2 SUV) extra-axillary nodes such as internal mammary and supraclavicular was associated with a non-statistically significant trend towards reduced RFS (p=0.06, HR=0.13-1.06). pCR overall was 37.5% for HER2 positive tumors, 15% in triple-negative tumors, and 8% in HR positive/HER2 negative tumors. Log-rank analysis with post-hoc pairwise comparisons showed a significant difference between the RFS of triple-negative tumors and HER2 positive tumors (p=0.001), while comparison between HR positive/HER2 negative and HER2 positive was not statistically significant (p=0.11). Multivariate cox regression analysis, which included grade and stage of tumors, showed HER2 positivity to be associated with a favorable outcome (p=0.04, HR=0.22 (0.05-0.94)). Conclusions: Within this cohort, pre-treatment SUV max of the primary tumor showed no prognostic value with regard pCR or RFS. PET avid extra-axillary metastasis trended towards reduced RFS. Patients with HER2 positive tumors had the highest pCR and RFS comparable to classically favorable subgroups such as HR positive/HER 2 negative.