Abstract 798: Increasing breast cancer incidence across generation status in Mexican American women: The Multiethnic Cohort

Abstract Background: Breast cancer (BC) is the most commonly diagnosed cancer among Latino women in the US. Compared to foreign-born Latino women, US-born Latino women have a higher incidence of BC. While prior studies have suggested this difference in incidence may be explained by risk factors such as unhealthy lifestyle behaviors, reproductive history, and neighborhood socioeconomic status, it is unclear how the risk of BC has changed over generations among Latinos women. In this study, we investigated the association between generational status and BC incidence among Mexican American women within the Multiethnic Cohort (MEC). Methods: The study population included 15, 303 self-reported Mexican Americans from the MEC. Generational status was categorized as: 1st generation (Mexico-born, n = 6, 347), 2nd generation (US-born with one or two parents born in Mexico, n = 6, 390), or 3rd generation (US-born with both parents born in the US, n = 2, 566). Multivariable Cox models were used to calculate the hazard ratios (HR) and 95% confidence intervals (CI) of BC incidence by generational status. All models were adjusted for relevant risk factors including age, physical activity, smoking, alcohol intake, education, body mass index, diet, family history of BC, menopausal status, age at menarche, parity, mammography history, hormone use, neighborhood socioeconomic status, and Hispanic ethnic enclave. Results: During an average 21. 5-year follow-up, 815 incident BC cases were identified. The age-adjusted incidence rate (per 100, 000) of BC increased by generation (1st: 191. 9; 2nd: 265. 3; 3rd: 284. 0). Third (70. 4%) and 2nd (66. 5%) generations had a larger proportion of localized disease at diagnosis compared to 1st generation women (59. 7%). Compared to 1st generation Mexican Americans, 2nd (HR = 1. 24; 95% CI: 1. 03-1. 49) and 3rd generation (HR = 1. 28; 95% CI: 1. 02-1. 60) had elevated risks of BC (p-trend: 0. 02) The positive association with generational status remained significant when restricting to women who reported mammogram use (HR 2nd vs. 1st = 1. 27, 95% CI: 1. 04-1. 55; HR 3rd vs. 1st = 1. 34, 95% CI: 1. 06-1. 70) (p-trend: 0. 01). Conclusions: Our findings suggest that generational status among Mexican American women is associated with risk of BC, after adjusting for sociodemographic, lifestyle, neighborhood, and reproductive risk factors. Further studies are warranted to discover the potential factors that contribute to this increased risk and elucidate the underlying etiology. Citation Format: Xinman Zhang, Iona Cheng, Adelynn Paik, Brian Huang, Veronica Wendy Setiawan. Increasing breast cancer incidence across generation status in Mexican American women: The Multiethnic Cohort abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 798.