Abstract P3-14-02: Racial/ethnic differences in the benefit of adjuvant chemotherapy for breast cancer patients with an intermediate risk 21-gene recurrence score

Abstract Background: The Oncotype 21-gene Recurrence Score (RS) is the most commonly ordered genomic biomarker used to inform decisions on adjuvant chemotherapy for patients with estrogen receptor (ER)-positive, HER2-negative early breast cancer. Representation of racial/ethnic minority patients in the population used to develop the assay was poor, with only 5% of study participants identified as Black. This raises concern about the accuracy of the RS in underrepresented populations. In earlier work (Hoskins et al, JAMA Oncology 2021), we showed that the RS has less prognostic accuracy in Black compared with non-Hispanic White (NHW) women. This finding is concerning in light of persistent racial disparities in breast cancer mortality. Here we examine the predictive accuracy of the RS according to race/ethnicity for identifying patients with ER+, axillary node-negative breast cancer who benefit from adjuvant chemotherapy.Methods: We conducted a large, population-based retrospective cohort study of women 18+ years diagnosed with ER+, axillary node-negative breast cancer from 2004 to 2010 using Surveillance, Epidemiology and End Results Oncotype DX Database (2004-2015). This analysis included women with a minimum of 7 yrs follow-up and an RS of 11-25, since this is the group with the most uncertainty regarding the benefit of chemotherapy. Demographic and clinical characteristics were collected from cancer registry data. Propensity score weighted Cox models determined the association between chemotherapy use and breast cancer death. Age, insurance status, tumor grade, tumor size, progesterone receptor status, and RS were included as predictors of the propensity score. Associations between chemotherapy use and breast cancer death were determined using overall, race/ethnicity, and age stratum-specific hazard ratios (HR) and 95% confidence intervals (CI). Results: The analysis included 22,693 NHW, 5,657 Black, and 3,348 Hispanic women. The overall result is consistent with the prospective TAILORx trial, showing greater benefit from chemotherapy in women under age 50. There is a greater reduction in the hazard of breast cancer death associated with chemotherapy use for Black (HR 0.31, 95% CI, 0.15, 0.66) and Hispanic (HR 0.07, 95% CI, 0.02, 0.31) compared with NHW women under age 50 (HR 0.43, 95% CI,0.32, 0.59). In models combining Black and NHW patients, an interaction term for race*chemotherapy was significant (p=0.022), indicating a differential association between chemotherapy use and breast cancer death according to race/ethnicity. Visual comparison of breast cancer mortality curves that plot 7-year breast cancer death rate as a function of the continuous RS, stratified by chemotherapy administration (yes/no), shows that the curves begin to diverge at a lower RS for Black (RS 17) compared with NHW women (RS 24). Conclusions: This observational study found that Black women under age 50 with ER+, axillary node-negative breast cancer and an RS of 11-25 derive significantly more benefit from adjuvant chemotherapy than NHW women. National practice guidelines do not recommend routine use of adjuvant chemotherapy for patients in this risk category, indicating that many Black patients may be undertreated. Results need to be confirmed in prospective studies, but they suggest that RS cut-offs used to recommend adjuvant chemotherapy may need to be modified for racial/ethnic minority women. Hazard of Breast Cancer Death (95% Confidence Interval)Race/EthnicityChemotherapyAll AgesAge < 50Age 50+OverallYes0.71 (0.63, 0.81)0.32 (0.25, 0.41)1.01 (0.87, 1.18)NoRefRefRefNHWYes0.73 (0.62,0.84)0.43 (0.32, 0.59)0.87 (0.74, 1.04)NoRefRefRefBlackYes0.83 (0.60, 1.16)0.31 (0.15, 0.66)1.26 (0.84, 1.89)NoRefRefRefHispanicYes0.33 (0.20, 0.57)0.07 (0.02, 0.31)0.61 (0.33, 1.12)NoRefRefRef Citation Format: Hsiao- Ching Huang, Gregory S. Calip, Jennifer Weiss, Yael Simons, V.K. Gadi, Oana C. Danciu, Garth H. Rauscher, Kent F. Hoskins. Racial/ethnic differences in the benefit of adjuvant chemotherapy for breast cancer patients with an intermediate risk 21-gene recurrence score [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-14-02.