Abstract 3670: Systematic literature review of risk factor associations with breast cancer subtypes in women of African, Asian, Hispanic, and European descents
Authors: Hurson Amber N. , Ahearn Thomas U. , Keeman Renske , Abubakar Mustapha , Jung Audrey Y. , Kapoor Pooja Middha , Koka Hela , Yang Xiaohong R. , Chang-Claude Jenny , Martínez Elena , Tamimi Rulla M. , Troester Melissa A. , Bandera Elisa V. , Schmidt Marjanka K. , Garcia-Closas Montserrat 
Published: June 2022

Abstract
Background: Studies have reported differences in associations between breast cancer risk factors and subtypes defined by hormone receptor status, particularly estrogen receptor (ER) positive versus ER negative tumors. Most studies have been conducted in women of European descent, and an expanding body of literature in other populations suggests differences by race/ethnicity. Clarifying whether associations between risk factors and disease subtypes are consistent across racial/ethnic populations has important implications for understanding disease etiology and for improving risk prediction models. To address this question, we conducted a qualitative literature review to investigate the consistency in associations between multiple breast cancer risk factors and risk of tumor subtypes in women of African, Asian, Hispanic, and European descent.
Methods: We searched PubMed for publications between January 1, 1990 and June 8, 2021 that reported associations between breast cancer risk factors and risk of subtypes of the disease. We evaluated 19 risk factors, including reproductive, anthropometric, lifestyle, and diet factors, as well as medical history and use of menopausal hormone therapy (MHT). Subtypes were defined as ER positive or negative (specifically triple negative when available). We prioritized review studies (i.e., meta-analyses, systematic reviews, and pooled analyses) and included individual studies with populations not included in the reviews. The number of publications per risk factor ranged from 3 for calcium intake to 28 for parity, with up to 7 reviews per risk factor. Most publications reported estimates for women of European descent, followed by Asian, African, and Hispanic. Evidence of subtype heterogeneity was determined by expert review.
Results: There was strong evidence of association between reproductive factors and MHT with risk of ER positive but not ER negative disease. Parity, younger age at first birth and older age at menarche were associated with lower risk of ER positive disease, while MHT use was associated with higher risk of ER positive disease. For these risk factors, we did not find evidence that risk associations or etiologic heterogeneity varied by race/ethnicity. For the other risk factors, there was limited or no evidence of heterogeneity in risk associations by subtype, which was consistent across racial/ethnic groups. Few publications, however, specifically studied women of non-European ancestry.
Conclusion: For most breast cancer risk factors, evidence is insufficient to evaluate differences in ER-specific risk associations by race/ethnicity. More studies are needed to evaluate subtype-specific breast cancer risk factors in diverse populations, which will be important for informing the development of multi-ethnic/racial BC risk prediction models that account for subtype heterogeneity.
Citation Format: Amber N. Hurson, Thomas U. Ahearn, Renske Keeman, Mustapha Abubakar, Audrey Y. Jung, Pooja Middha Kapoor, Hela Koka, Xiaohong R. Yang, Jenny Chang-Claude, Elena Martínez, Rulla M. Tamimi, Melissa A. Troester, Elisa V. Bandera, Marjanka K. Schmidt, Montserrat Garcia-Closas. Systematic literature review of risk factor associations with breast cancer subtypes in women of African, Asian, Hispanic, and European descents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3670.