Abstract B068: Predictors of estrogen receptor staining levels in African American women with ER+ breast cancer in the Detroit Research on Cancer Survivors study

Abstract Introduction: Breast cancer incidence in African American women (AAW) in the U.S. is now equal to that in European American women (EAW). Despite having the highest survival rates of all breast cancer subtypes, AAW are nearly twice as likely to die from hormone receptor-positive (HR+) disease compared to EAW. ER+/HER2- breast cancer is a heterogeneous subtype, with tumors showing anywhere from 1-100% ER staining by immunohistochemistry. AAW are also more likely to have a lower proportion of HR+ cells within their breast tumor compared to EAW, and tumors with lower proportions of HR+ cells are associated with worse survival. While this is consistent with the fact that AAW are more likely to have aggressive breast cancer subtypes like triple negative breast cancer, our understanding of epidemiologic risk factors associated with various levels of ER staining is limited particularly among scientifically underrepresented populations. Therefore, our objective was to identify predictors associated with estrogen receptor staining levels in AAW. Methods: Questionnaire and population-based registry data from 748 female HR+ breast cancer survivors enrolled in the Detroit Research on Cancer Survivors (ROCS) study were analyzed. Risk factors of interest included self-reported demographics, socioeconomic characteristics, and health behaviors. Individual and combined estrogen receptor (ER) and progesterone (PR) percent staining levels were obtained from medical record review. A combined hormone report (HR) staining level variable was created based on the maximum percent staining among ER and PR. Associations between risk factors and HR staining levels were evaluated using chi-squared tests, and univariable and multivariable linear regression. An alpha value of 0.05 was set to determine statistical significance. Results: In our cohort, a majority of patients (86.6%), had tumors that were characterized as high HR staining (>90% of tumor cells HR+). A small percentage of tumors were found to be in the low (1-10% HR+: 6.6%) or medium (11-90% HR+: 6.8%) staining categories. When looking at each variable individually, we saw that demographic and medical history variables were associated with percent HR staining levels, including, age at diagnosis (beta=0.038,p<0.001), diabetes (beta=0.052,p= 0.03), high blood pressure (beta=0.060,p= 0.0037) and high cholesterol (beta=0.052,p= 0.028). When stratified by HER2 status, these associations remained similar in effect size and statistical significance only among HER2- patients. In a multivariable model, percent HR staining was associated with age at diagnosis (beta=0.002,p= 0.031), HER2+ status (beta= -0.15, p<0.001), marital status (beta= -0.016,p= 0.084) and nulliparity (b=0.073,p=0.012). Conclusions: Our findings identify multiple risk factors that are associated with weakly positive ER tumors. As AAW die more frequently from ER+/HER- weak breast cancers, these findings have potential application in improving future screenings and providing optimal therapeutics, resulting in a better prognosis among this cohort. Citation Format: Abigail M. Fielder, Jaclyn Kyko, Mrudula Nair, Julie Ruterbusch, David Gorski, Michael Simon, Lauren Hamel, Ann G. Schwartz, Kristen S. Purrington. Predictors of estrogen receptor staining levels in African American women with ER+ breast cancer in the Detroit Research on Cancer Survivors study [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr B068.