Abstract PS4-12-12: Racial Disparities in Pathologic Complete Response in Patients with HER2 Positive Breast Cancer Treated with Neoadjuvant Chemotherapy

Abstract Background: Black patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancers have lower rates of pathologic complete response (pCR) following neoadjuvant chemotherapy (NAC). This study aims to identify factors that contribute to disparities in achieving a pCR in HER2-positive breast cancers. Method: A retrospective review of an institutional tumor registry identified women with HER2-positive breast cancers who underwent NAC followed by surgery from 2016 to 2022. Sociodemographic factors, clinicopathologic features, and treatment variables were compared between patients self-identified as Black, White, and Other. Results: The study included 445 women with a median age of 54 (range 22-86) and a median follow-up of 48 months (range 7-110). A total of 355 (79.8%) self-identified as White, 58 (13.0%) Black, and 32 (7.2%) Other. There were no differences in Charlson Comorbidity Index, type of insurance, hormone receptor status, HER2 immunohistochemical score, clinical stage, overall grade, chemotherapy regimen, and completion of chemotherapy between racial groups. There was no difference in median number of days from diagnosis to initiation of chemotherapy or median number of days from completion of chemotherapy to surgery between racial groups (Black = 30.5, White = 30, Other = 31.5 p=0.85 and Black = 22, White, 19, Other = 21 p=0.26). Following NAC, Black patients achieved a pCR in both the breast and axilla less frequently than White patients or Other (24 41% Black patients, 191 54% White patients, 20 63% Other), although this difference was not statistically significant (p=0.11). Factors associated with achieving pCR included age of diagnosis 50 years (p=0.02), private insurance (p=0.02), hormone receptor-negative tumor subtype (p0.001), HER2 immunohistochemical score of 3+ (p=0.001), and grade 3 disease (p=0.01). Race, Charlson Comorbidity Index, tumor histology, clinical stage, and chemotherapy regimen were not associated with achieving pCR. Conclusion: Black patients had the lowest rate of pCR compared to patients self-identified as White or Other, although this difference was not statistically significant. The higher likelihood of Black patients being diagnosed with HER2-positive breast cancer at ≥50 years may account for the differences in achieving a pCR, however more research to understand disparities in outcomes are needed. Citation Format: R. Matar-Ujvary, R. Rangan, W. Wei, Z. Al-Hilli. Racial Disparities in Pathologic Complete Response in Patients with HER2 Positive Breast Cancer Treated with Neoadjuvant Chemotherapy abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-12-12.