Abstract C019: Peripheral Absolute Lymphocyte Count and Breast Cancer Mortality among Racially Diverse Women

Abstract Background: Among patients with triple-negative breast cancer (TNBC), higher tumor infiltrating lymphocytes (TILs) are associated with increased overall mortality (OM) and breast cancer-specific mortality (BCSM). We previously found that low peripheral absolute lymphocyte count (ALC) is associated with increased OM and BCSM in a sample of mostly non-Hispanic White (NHW) patients with TNBC. Here, we investigated the association between low ALC and mortality (OM and BCSM) across different breast cancer subtypes and whether the association is potentially modified by race and ethnicity. Methods: We used the Oncoshare database, which links electronic medical records (EMRs) data to the California Cancer Registry (CCR), and assessed women diagnosed with stage I-III breast cancer between 2000-2017, who had at least one ALC measurement and treated at two healthcare systems in California. Patient and tumor characteristics were obtained from the CCR and laboratory testing from EMRs. Patients with metastatic disease and chemotherapy receipt after one year of diagnosis were excluded. Multivariable logistic models assessed factors associated with “low ALC” (<1 K/µL, ever vs. never). We applied Cox models to evaluate the association between “min ALC” (lowest ALC value after diagnosis) and OM and BCSM within each breast cancer subtype (Luminal A, HER2-enriched, and TNBC), and further explored the interaction between min ALC and race and ethnicity. All models adjusted for low absolute neutrophil count, demographics, and tumor features. Results: Among 10,750 women analyzed, the risk of “low ALC” was associated with TNBC vs Luminal A (odds ratio (OR) 1.22, p=0.0098), older age (OR 1.01 per year, p<0.001), higher grade (grade 3 vs. 1, OR 1.15, p=0.042), higher stage (stage III vs. I, OR 1.81, p<0.001), and public vs. private health insurance (OR 1.29, p<0.001). Cox models showed that higher min ALC was associated with lower OM across breast cancer subtypes (Luminal A: HR 0.37, HER2-enriched: HR 0.32, TNBC: HR 0.22; all p<0.001) and BCSM (Luminal A: HR 0.29, HER2-enriched: HR 0.23, TNBC: HR 0.19; all p<0.001). Interaction analysis showed that race and ethnicity modified the association between min ALC and OM (interaction-p <0.001) and BCSM (interaction-p < 0.001) in the overall cohort; compared to NHW women (HR 0.38, 95% confidence interval [0.34-0.43]), the association between min ALC and OM was stronger among Hispanic (HR 0.24, [0.18-0.33]), Asian (HR 0.19, [0.14-0.25]), and Black (HR 0.21, [0.13-0.35]) women. Similar results were observed for BCSM. Conclusions: Low peripheral ALC, a routinely measured clinical lab result, strongly predicts higher BCSM and OM across breast cancer subtypes, beyond TNBC. The association between min ALC and BCSM/OM was stronger among Black and Asian women vs. NHW women, suggesting that maintaining normal ALC during breast cancer treatment may reduce BCSM and OM, especially for women from racial and ethnic minoritized groups. Future research should investigate differences in ALC, immune response, and BCSM in diverse populations. Citation Format: Candice N. Thompson, Ingrid Luo, Mina Satoyoshi, Lidia Schapira, Esther M. John, Summer S. Han, Allison W. Kurian. Peripheral Absolute Lymphocyte Count and Breast Cancer Mortality among Racially Diverse Women [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C019.