Background Transcriptomic immune-related gene signatures have been associated with achievement of pathologic complete response (pCR) and prognosis in the neoadjuvant setting. I-SPY 2 is a multicenter, phase 2 platform trial using response-adaptive randomization within subtypes defined by receptor status (HR/HER2) and MammaPrint (MP) risk to evaluate novel agents as neoadjuvant therapy for women with high-risk breast cancer. Given racial disparities in mortality from breast cancer and the paucity of racial demographic data from clinical trials, we aimed to evaluate the association between racial groups and baseline characteristics, including expression-based subtypes and immune signatures, treatment response, and prognosis of patients enrolled in the I-SPY 2 TRIAL.

‍Methods Our study population included 990 I-SPY 2 patients. 15 patients identified as part of a racial group with <10 patients enrolled in the trial and were excluded from analysis. Pre-treatment expression data was available for 971 patients. Follow-up data was available for 907 patients; median follow-up time of 4.4 yrs. Chi-square test was used to assess associations between racial groups and pre-treatment SBR grade, HR/HER2 defined subtypes, intrinsic subtype (defined by BluePrint 80-gene molecular subtyping) and residual cancer burden (RCB) class. Logistic regression was used to evaluate race association with pCR. Cox proportional hazard modeling was used to assess the association between racial groups and event free survival (EFS) in a univariate setting, adjusting for pCR status. Association between racial groups and 28 expression signatures related to immune, proliferation, ER and HER2 pathway was analyzed using ANOVA with post-hoc Tukey test in the overall population and in each receptor subtype.

‍Results Of 975 patients included in our analysis, 787 (81%) were White, 68 (7%) were Asian, and 120 (12%) were Black or African American. No significant associations between race and pre-treatment SBR grade (p=0.49), HR/HER2 defined subtypes (p=0.09), or expression-based subtypes (p=0.25) were observed. pCR rates do not significantly differ by racial groups (Odds ratio of pCR relative to White: 1.00 for Asian and 0.89 for Black or African American); and no significant differences in RCB class distribution by race was observed (p=0.88). Event free survival was not associated with patient racial group in a univariate Cox model (Hazard ratio relative to White: 1.10, p=0.73 for Asian and 1.37, p=0.13 for Black or African American). Among the 28 expression signatures evaluated, four were differentially expressed among racial groups within the overall population (F-test p<0.05): IFN module, B cell signature, Dendritic cell signature, and Mitotic score. Pairwise comparisons between racial groups with post-hoc Tukey test identified significant differences in IFN module expression between Black or African American vs. White (p=0.019) and Dendritic cell signature expression between Asian vs White (p=0.047). Among patients in the TNBC subtype, three signatures (dendritic cell signature, macrophage signature and ERBB2 module) were differentially expressed between Black or African American and White patients (p=0.002, 0.016 and 0.007).

‍Conclusion Our analysis demonstrates that among women with high risk breast cancer, race does not affect subtype specific response rates nor event free survival. Distribution of subtypes previously shown to be associated with pCR in the I-SPY2 trial did not significantly differ among racial groups indicating race is less likely than tumor biology to predict response. The decreased expression of immune signatures observed in Black or African American women with TNBC suggests possible differential sensitivity to immunotherapy plus combination chemotherapy. Tumor immune multiplex studies are underway to further investigate.