Racial differences in the prognostic value of Oncotype (RS) and MammaPrint (MP) in postmenopausal, estrogen receptor (ER)–positive, node-negative (N0) breast cancer (BC) patients with low genomic risk: A National Cancer Database (NCDB) study.

539 Background: Postmenopausal patients with ER+, HER2 negative, N0 BC often rely on genomic testing, such as RS or MP, to determine the benefit of chemotherapy. However, the prognostic value of RS, particularly among ethnic minority patients, remains uncertain. Methods: We utilized the 2021 NCDB to include postmenopausal female BC patients aged >50 years. Inclusion criteria were ER+, HER2-negative patients with, stage T1-4, N0, RS <26, or MP low risk. Patients were stratified by race, Caucasian (W) and African American (AA). Univariate analysis was performed to evaluate patient and tumor characteristics. Five-year overall survival (OS) rates were constructed using Kaplan-Meier (KM) product limit estimation. Unadjusted and covariate adjusted associations between race and OS were evaluated using Cox proportional hazard (PH) regression. Associations between race and OS among subgroups were similarly evaluated to highlight disparities and trends within the population. Hazard ratios (HRs; AA: W), 95% confidence intervals (CIs) and p-values are reported. Results: 96,411 patients had an RS<26 [W- 89,105 (92.42%) AA-7,306(7.58%)] and 3,146 had MP low [W-2,929(93.1%) AA-217(6.9%)]. Over 93% of patients in both groups received endocrine therapy, ~75% underwent partial mastectomy and radiation, and 7% received chemotherapy. Significant racial differences in tumor size and grade were observed in the RS group: T1 tumors (AA: 75% vs. W: 78%), T2 tumors (AA: 23% vs. W: 20%, p<0.001), G1 (AA: 29% vs. W: 34%), and G3 (AA: 13% vs. W: 9.3%, p<0.001), but these differences were not seen in the MP group. At 5 years, survival for RS <26 was 95.5% (AA) vs. 97.1% (W), and for MP low, 96% (AA) vs. 96.7% (W). The adjusted HR for RS <26 showed worse outcomes for AA (HR: 1.2, 95% CI 1.1–1.31, p<0.001), especially in younger patients, grades 1–2 tumors, T1 stage, partial mastectomy and low income. For MP low, the HR was not significant (HR: 1.08, 95% CI 0.59–1.97, p=0.8). Conclusions: Our analysis shows that among ER+, HER2- N0 cohort with RS <26, AA patients have a 20% increase in the risk of death compared to W patients, after adjusting for patient- and tumor-related factors. In contrast, no survival disparities were observed in the MP low-risk group. These findings suggest that RS may not be fully prognostic for AA patients even when accounting for clinic-pathologic risk factors. Study limitations include its retrospective design, potential biases, and incomplete consideration of biological and socioeconomic factors.