Abstract PO-151: Risk factors associated with breast cancer subtypes among Black women that have undergone screening mammography

Purpose: This study explores the associations of breast density and reproductive risk factors with invasive breast cancer subtypes in Black women. Background: Well- established risk factors for breast cancer have been extensively studied in White populations but fewer studies have examined these factors in Black populations. Black women are more likely to be diagnosed with triple negative breast cancer (TNBC), a more aggressive subtype with poorer prognosis than estrogen receptor (ER) and/or progesterone receptor (PR) positive, HER2 negative (ER/PR+HER2-) breast cancer. This study assesses the associations of breast density and reproductive risk factors with ER/PR+HER2- and TNBC subtypes among Black women. Methods: Black women who underwent screening mammography at the University of Pennsylvania between 2010-2015 were included. Eligible women were older than 40 years, had no prior breast cancer, no breast implants, and no known BRCA1/2 mutation. Data collection included a questionnaire completed at the time of screening and electronic medical records abstraction. Outcomes of interest included invasive breast cancer subtypes: ER and/or PR+ HER2-, TNBC, as determined by immunohistochemistry. Women were censored at death, date diagnosed with DCIS or another subtype of breast cancer, or on December 31, 2017 if they were alive and cancer free. Known breast cancer risk factors examined included age at screening, age at menarche, breast density (extremely or heterogeneously dense vs. scattered or almost entirely fatty), family history, BMI, and parity. Among parous women, age at first live birth, number of births and any history of breastfeeding were examined. Cox proportional hazard models were used to estimate hazard ratios and 95% confidence intervals. Results: Among 24,857 Black women, mean age was 56.2 (40- 84) and 268 (1%) developed invasive breast cancer during a mean follow up of 4.32 years; 179 (67%) of those cancers were ER/PR+ HER- and 51 (19%) were TNBC. Factors found to increase risk across both subtypes included family history and dense breasts. Having dense breasts increased risk of ER/PR+ HER2- breast cancer by over 70% (HR: 1.73, 95%CI 1.24-2.40)) and TNBC more than twofold (HR: 2.57, 1.40-4.72). Among ER/PR+/HER2-breast cancers, older age at menarche was protective (>=14 vs =14 vs. In addition, later age at menarche was associated with increased risk of TNBC but protective for ER/PR+HER2- disease. These results highlight the importance of assessing risk factors for tumor subtypes in Black women. Citation Format: Tara Friebel, Sarah Ehsan, Susan Domchek, Despina Kontos, Emily Constant, Anne Marie McCarthy. Risk factors associated with breast cancer subtypes among Black women that have undergone screening mammography [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-151.