Breast cancer incidence and stage at diagnosis in the six US-Affiliated Pacific Islands

Background: Breast cancer is the most common cancer diagnosed among women globally and in the United States (US); however, its incidence in the six US-Affiliated Pacific Islands (USAPI) remains less characterized. Methods: We analyzed data from a population-based cancer registry using different population estimates to calculate incidence rates for breast cancer among women aged >20 years in the USAPI. Rate ratios and 95 % confidence intervals (CI) were calculated to compare incidence rates between the USAPI and the US (50 states and the District of Columbia). Results: From 2007-2020, 1118 new cases of breast cancer were diagnosed in the USAPI, with 66.3 % (n = 741) of cases reported in Guam. Age-standardized incidence rates ranged from 66.4 to 68.7 per 100,000 women in USAPI and 101.1-110.5 per 100,000 women in Guam. Compared to the US, incidence rates were lower in USAPI, with rate ratios ranging from 0.38 (95 % CI: 0.36, 0.40) to 0.39 (95 % CI: 0.37, 0.42). The proportion of late-stage cancer was significantly higher in the USAPI (48.7 %) than in the US (34.0 %), particularly in the Federated States of Micronesia (78.7 %) and Palau (73.1 %). Conclusions: Breast cancer incidence rates were lower in the USAPI than in the US; however, late-stage diagnoses were disproportionately higher. Low incidence and late-stage cancers may signal challenges in screening, cancer surveillance, and health care access and resources. Expanding access to timely breast cancer screening, diagnosis, and treatment could reduce the proportion of late-stage cancers and improve survival in the USAPI.