Background: Mammographic density is an important breast cancer risk factor, yet data on mammographic density is limited for some racial/ethnic groups, including Native Hawaiians and Pacific Islanders (NHPI). Obesity is highly prevalent in the NHPI population and prior work, primarily in non-Hispanic White (NHW) women, has reported that high body mass index (BMI) is inversely associated with mammographic density but positively associated with risk of breast cancer. We used data from the Utah Population Database (UPDB) to estimate the association between BMI and mammographic density in Utah's NHPI population and evaluate if the association differs for NHPI women compared to NHW women.

Methods: We included women ages 18-79 years with at least one mammogram from 2005-2012 and no history of breast cancer. Data on BMI and race/ethnicity were collected from the UPDB, and mammographic density was evaluated using Breast Imaging Reporting and Data System (BIRADS) scores. We estimated the association between BMI and BIRADS using multinomial logistic regression adjusted for age and stratified at age 55 (a proxy for menopausal status). Heterogeneity by race/ethnicity was evaluated using likelihood ratio tests.

Results: Our analyses included data from 102 Native Hawaiian, 112 Samoan, 344 other Pacific Islander, and 143,259 NHW women. High mammographic density (BIRADS=4) was less common among Samoan women (2.7%) and other Pacific Islanders (4.7%) compared to NHW women (5.8%), but more common among Native Hawaiians (11.8%). Age-standardized BMI was highest in Samoan women (mean=32.3, SD=6.3) followed by other Pacific Islander women (mean=31.2, SD=7.1) then Native Hawaiian women (mean=27.8, SD=6.4), and lowest among NHW women (mean=26.1, SD=5.4). Among women younger than age 55, a one-unit increase in BMI was associated with 0.76 (95% CI=0.69-0.84) times lower odds of high (BIRADS=4) versus low (BIRADS=1) breast density in NHPI women. The comparable odds ratio (OR) in NHW women was 0.66 (95% CI=0.65-0.66; p-heterogeneity=6.9 × 10^-10). For women age 55 and older, the association between BMI and mammographic density was stronger among NHPI women, OR=0.62 (95%CI=0.45-0.84), compared to NHW women, OR=0.70 (95%CI=0.69-0.72; p-heterogeneity=0.018).

Discussion: Mammographic density differs among racial/ethnic subgroups of the NHPI population with Native Hawaiians having the highest mammographic density. Given the high prevalence of obesity in the NHPI population and evidence that the association between BMI and mammographic density may differ by race/ethnicity, more research is needed to understand how BMI and mammographic density influence risk of breast cancer in understudied racial/ethnic minorities, such as NHPIs.

Citation Format: Mollie E. Barnard, Tarun Martheswaran, Jennifer A. Doherty, Karen Curtin. Body mass index and mammographic density among Native Hawaiians and Pacific Islanders [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3485.