Abstract 1029: Prevalence of mammographically dense breasts in Guam

Abstract Background: Breast cancer is the most diagnosed cancer among women in Guam. Mammographic breast density is a critical factor in assessing breast cancer risk and the effectiveness of screening. Guam’s female population is diverse, comprising CHamoru (37.3%), Filipino (26.3%), Mixed (9.5%), White (7.1%), Chuukese (7%), and other Pacific Islander and Asian ethnicities. Understanding breast density patterns among these groups is essential for developing tailored public health strategies. However, specific data on the distribution of breast density among women in Guam is currently lacking. This study, conducted through the Hawai‘i and Pacific Islands Mammography Registry (HIPIMR), addresses this gap by estimating the prevalence of dense breasts among women in Guam aged 40 years and older. Methods: The mammographic breast density distribution by age and body mass index (BMI) was determined using data from 1, 940 mammograms conducted at the FHP Health Center in Guam between October 2023 and September 2024 for women aged 40 and older (N = 1, 920). These breast density distributions were applied to age- and BMI-specific counts of the female population in Guam, derived from the 2020 Guam Census and the Guam Behavioral Risk Factor Surveillance System (BRFSS), to estimate the number of women with dense breasts. Ethnic variations in breast density distributions were examined using a chi-square test. Results: Among the 1, 920 women analyzed, breast density was categorized as BI-RADS A (9.2%), BI-RADS B (19.2%), BI-RADS C (17.2%), and BI-RADS D (54.1%). BMI distribution included under/normal weight (27.2%), overweight (26.7%), obese (31.2%), and cases with missing BMI data (14.9%). Filipino (81.1%) and Asian (84.0%) women had significantly higher combined proportions of dense breasts compared to CHamoru (63.6%) and Micronesian (52%) women (P < 0.001).Overall, 74.8% (95% CI: 74.3%-75.3%) of women aged 40-74 in Guam were classified as having heterogeneously or extremely dense breasts with the prevalence inversely associated with age and BMI. Based on the age and BMI distribution of Guam’s female population, an estimated 22, 185 (95% CI: 22, 043-22, 340) women aged 40-74 have heterogeneously or extremely dense breasts, with women aged 40-49 accounting for 82.5% of this group. Conclusion: The prevalence of dense breasts among women in Guam is high (74.8%) compared to approximately 43% in the U.S., with Filipino and Asian populations showing the highest proportions. These findings underscore the need for breast density notification policies and enhanced access to supplemental screening for high-risk groups to improve early detection in Guam’s diverse population. Acknowledgement: This research was funded by the National Cancer Institute: The University of Guam/University of Hawaii Cancer Center Partnership to Advance Cancer Health Equity, Grant U54CA143728 (University of Guam, YCP)/Grant U54CA143727 (University of Hawaii Cancer Center). Citation Format: Prevalence of mammographically dense breasts in Guam. Reina Faye P. Evangelista, Louis Jane B. Dulana, Rodney Teria, Su Bin Jin, Gian Paras, Rose Grino, John Shepherd, Grazyna Badowski [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1029.