Abstract LB312: Subtype- and race-specific differences in immune landscape of breast cancer

Abstract Tumor mass comprises of not just the tumor cells but a variety of stromal cells. Immune cells residing within the tumor microenvironment modulate the growth and behavior of the tumor cells through a bi-directional crosstalk and affect the outcomes of cancer therapies. Breast cancer (BC) is a highly heterogeneous disease having four major molecular subtypes. Triple-negative breast cancer (TNBC) is the most aggressive subtype and has limited available therapeutic options. Further, it disproportionately affects African American (AA) women, with nearly two times higher incidence as compared to Caucasian American (CA) women. It is associated with an earlier onset and overall higher mortality of BC. Here, we investigated the differences in the immune landscape between TNBC and non-TNBC subtypes and examined if there existed any race-specific patterns. A total of 81 breast cancer samples with a distribution of 55 non-TNBC (28 CA and 27 AA) and 26 TNBC (12 CA and 14 AA) were selected after histopathologic analysis. Tissues were analysis using the NanoString nCounter® pancancer immune panel to determine tissue-specific immune cell populations. We observed a significantly higher presence of tumor-infiltrating lymphocytes in TNBC compared to non-TNBC, with a higher immune score for CD45+ (total lymphocytes), T-cells, B-cells and tumor-associated macrophages. Specifically, among the T-cell population, Treg cells, Th1 cells, and CD8+ cells were higher in TNBC samples. The pathway prediction indicated 'primary immunodeficiency' and 'cancer immunotherapy by PD-1 blockade' pathways being significantly up-regulated in TNBC samples. Overexpression of CTLA4, IDO1, PDL1 and PDL2 as well as Treg marker genes, such as FOXP3 and LAG3, which are involved in immunosuppressive pathways, was observed in TNBC. In race-wise comparisons of non-TNBC and TNBC sample between CA and AA patients, we found that AA non-TNBC tumors had higher Treg cell scores. On the other hand, CA TNBC samples had higher Th1 and CD8+ T-cell scores compared to AA TNBC. The pathway prediction from differentially expressed genes between CA and AA non-TNBC samples showed complement activation pathway to be down-regulated in AA patients, which could be associated with an increased presence of Treg cells. Further, when comparing CA vs AA TNBC samples, we found significant up-regulation of oncogene BMI1 and down-regulation of genes involved in T-cell activation such as CD47, CD44, FOS, and S100A8 in AA TNBC, supporting their more aggressive nature. In conclusion, our data show that TNBC patients have a higher infiltration of immune cells, which remain suppressed due to the presence of Treg cells and PD1 signaling pathway. The presence of higher Treg cells in AA non-TNBC and lower Th1 and CD8+ T-cells in AA TNBC samples suggests an overall immune suppressed microenvironment in AA patients compared to CA patients. Overall, our data suggest that TNBC could be good candidate for immune therapy. Citation Format: Amod Sharma, Kunwar Somesh Vikramdeo, Sarabjeet Kour Sudan, Mohammad Aslam Khan, Mohammad Tahir, James Elliot Carter, Cindy Nelson, Ajay P Singh, Seema Singh. Subtype- and race-specific differences in immune landscape of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB312.