Abstract 6125: Differential expression of chemokine genes by race and Breast Cancer Consensus Subtypes in hormone receptor positive breast cancer

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Abstract Hormone receptor positive (HR+) breast cancer is a heterogeneous subtype and African American women (AAW) are twice as likely to have HR+ tumors with lower levels of HR staining (1-10%) compared to European American women (EAW). These tumors are associated with substantially worse survival compared to strongly HR+ tumors. We further hypothesized that HR+ tumors from AAW would be more likely to have molecular features typically associated with HR-negative breast cancer and poor prognosis. To test this, we used the Breast Cancer Consensus Subtyping (BCCS) method and evaluated expression of chemokine receptors known to be differentially expressed by race, PAM50 subtypes, and survival. We downloaded The Cancer Genome Atlas (TCGA) expression data for 394 female EA and AA HR+/HER2- breast cancer patients using the cBio Cancer Genomics Portal. Breast Cancer Consensus Subtypes (BCCS) were determined using the R program BCCSclassifier. BCCS classification results in five subtypes: ER-negative non-basal-like (BCS1), ER-negative basal-like (BCS2), ER+ highly proliferative with poor prognosis (BCS3), ER+ stromal infiltration with good prognosis (BCS4), and ER+ hormone response genes highly expressed with good prognosis (BCS5). High and low expression of chemokines (ACKR1, ACKR4, CCR3, CCR6, CCRL2, CXCR1, CXCR2, CXCR4, CXCR6, CX3CR1) was dichotomized based on median expression of each gene within our study cohort. Distribution of BCCS by race was assessed with multinomial logistic regression. Associations between chemokine gene expression, BCC subtype and race were evaluated using logistic regression. An alpha value of 0.05 was set to determine statistical significance. From the TCGA cohort, AAW were more likely to have the BCS2 ER-negative basal-like phenotype (OR=7.17, p<0.001) as well as the poor prognosis highly proliferative ER+ BCS3 phenotype (OR=2.83, p=0.036) versus the high hormone expression BCS5 subtype. In multivariable models evaluating both race and BCCS subtype, AAW were 6.17 times more likely to have lower than median expression of CX3CR1 (p<0.001) and CXCR2 (OR=2.23, p=0.0096) compared to EAW. Notably, all chemokine receptors consistently showed significantly lower expression in BCS1-4 subtypes compared to BCS5. For CCRL2, the effect estimates for BCS4 vs. BCS5 significantly differed by race (p=0.039). In AAW, BCS4 was associated with higher than median expression (OR=1.99, p=0.49), although not statistically significant. In EAW, BCS4 was associated with lower than median expression (0.23, p<0.001). Our findings show that AAW with HR+ breast cancer have tumors with more inherently aggressive molecular subtypes associated with poor prognosis compared to EAW. These results also further support the premise that HR+/HER2- tumors are highly heterogeneous and strongly suggest that chemokine gene expression is associated with breast cancer subtype. Citation Format: Abigail M. Fielder, Manohar Ratnam, Gregory Dyson, Kristen Purrington. Differential expression of chemokine genes by race and Breast Cancer Consensus Subtypes in hormone receptor positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6125.