Abstract 1937: Racial differences of epigenome in normal breast tissue reveal biological pathways implicated in racial disparities in breast cancer

Abstract

Abstract Racial disparity in breast cancer is well recognized. Compared to European American (EA) women, African American (AA) women are more often diagnosed with breast cancer at younger ages, have a more advanced or aggressive disease, and have poorer outcomes. Increasing evidence suggests that biological differences between EA and AA women, particularly differences in epigenetic changes of DNA methylation (DNAm), may contribute to the observed cancer disparity. We hypothesize that racial differences in DNAm in normal breast tissue may reflect distinct genomic susceptibility to breast cancer in different racial groups. Therefore, we investigated epigenome-wide differences of DNAm in normal breast tissue between 178 EA and 272 AA women using the Illumina TruSeq Methyl Capture EPIC library and NGS technology. We identified 17,340 differentially methylated CpG loci (DMLs) between EA and AA women, of which 7,744 were hypermethylated in AA women and 9,596 were hypermethylated in EA women. Pathway analyses of genes annotated to these racial DMLs suggested enrichment of biological processes including cell movement, cell motility, and cell migration, features that are likely linked to the aggressiveness and metastatic potentials of tumor cells. We further examined racial differences in DNAm of breast cancer-related candidate genes and GWAS-identified breast cancer risk loci. Approximately 30% of candidate genes were found to have racial differences in DNAm at more than three CpG sites and these candidate genes were enriched for pathways related to response to stimulus and anatomic structure development. Most interestingly, racial DMLs were found to be enriched for breast cancer risk loci that are associated with risk of estrogen-receptor negative (ER-) breast cancer, treatment response to aromatase inhibitor, and breast cancer-specific morality, phenotypes of which we observed differences between EA and AA breast cancer patients. Our results suggest that racial differences in DNAm in normal breast tissue may induce different biological processes that lead to distinct clinical features of breast tumors observed in EA and AA women and provide an epigenetic mechanism underlying the observed racial disparities. Further research is need to validate the findings of this study. Citation Format: Nan Lin, James Castle, Jinpeng Liu, Chunyan He. Racial differences of epigenome in normal breast tissue reveal biological pathways implicated in racial disparities in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1937.