Abstract PS18-10: Tumor-Infiltrating Lymphocytes and Breast Cancer Mortality in Racially and Ethnically Diverse Participants of the Northern California Breast Cancer Family Registry

Abstract Purpose: Greater stromal tumor-infiltrating lymphocyte (sTIL) percentage in pre-treatment breast tumor specimens is associated with superior response to neoadjuvant chemotherapy and survival. We hypothesized that sTIL-survival associations vary by race and ethnicity and mediate survival disparities. Patients and Methods: We evaluated pre-treatment percentages of sTILs in deciles for 284 women enrolled in the Northern California Breast Cancer Family Registry and diagnosed with a first primary invasive breast cancer from 1995-2005. We assessed associations of continuous sTIL scores and lymphocyte-predominant breast cancer (LPBC, defined as ≥50% lymphocytic infiltration of tumor stroma or cell nests) with clinical and epidemiologic characteristics using regression analysis and with breast cancer-specific mortality (BCM) and overall mortality (OM) using Cox proportional hazards regression. Results: The cohort was diverse (64% from racially and ethnically minoritized populations) with near-complete (98%) germline BRCA1/2 testing and long-term follow-up (average 16.2 years, range: 1.3-26.7). In multivariable analyses, higher sTIL score was associated with reduced BCM LPBC versus non-LPBC: HR=0.44 (95% confidence interval 0.20-0.98); and per decile increase in sTIL score: HR=0.80 (0.69-0.93), with the strongest association in the subset of patients with hormone receptor-negative disease HR=0.71 (0.57-0.88) and HR=0.37 (0.14-0.94), respectively. While there was no significant difference in sTIL score between racial and ethnic groups, the continuous sTIL-survival association was statistically significant among non-Hispanic White HR=0.73 (0.57-0.94) and Asian American HR=0.56 (0.35-0.89) women but was not seen among African American and Hispanic women. Conclusion: We identified novel sTIL-BCM differences by race and ethnicity, with better survival associated with sTIL enrichment among non-Hispanic White and Asian American but not among African American or Hispanic women. Additional studies are needed to determine whether survival and particularly the response to immunotherapy are differentially mediated by immune factors between racial and ethnic groups. Multivariable Cox Proportional Hazards Regression Models of Breast Cancer-Specific and Overall Mortality. Citation Format: Julia Ransohoff, Iain Miller, Jocelym Koo, Vishal Joshi, Allison Kurian, Kimberly Allison, Esther John, Melinda Telli. Tumor-Infiltrating Lymphocytes and Breast Cancer Mortality in Racially and Ethnically Diverse Participants of the Northern California Breast Cancer Family Registry abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS18-10.