Risk of contralateral breast cancer among Asian/Pacific Islander women in the United States.

Purpose: While breast cancer studies often aggregate Asian/Pacific Islander (API) women, as a single group or exclude them, this population is heterogeneous in terms of genetic background, environmental exposures, and health-related behaviors, potentially resulting in different cancer outcomes. Our purpose was to evaluate risks of contralateral breast cancer (CBC) among subgroups of API women with breast cancer.

Methods: We conducted a retrospective cohort study of women ages 18 + years diagnosed with stage I-III breast cancer between 2000 and 2016 in the Surveillance, Epidemiology and End Results registries. API subgroups included Chinese, Japanese, Filipina, Native Hawaiian, Korean, Vietnamese, Indian/Pakistani, and other API women. Asynchronous CBC was defined as breast cancer diagnosed in the opposite breast 12 + months after first primary unilateral breast cancer. Multivariable-adjusted subdistribution hazard ratios (SHR) and 95% confidence intervals (CI) were estimated and stratified by API subgroups.

Results: From a cohort of 44,362 API women with breast cancer, 25% were Filipina, 18% were Chinese, 14% were Japanese, and 8% were Indian/Pakistani. API women as an aggregate group had increased risk of CBC (SHR 1.15, 95% CI 1.08-1.22) compared to NHW women, among whom Chinese (SHR 1.23, 95% CI 1.08-1.40), Filipina (SHR 1.37, 95% CI 1.23-1.52), and Native Hawaiian (SHR 1.69, 95% CI 1.37-2.08) women had greater risks.

Conclusion: Aggregating or excluding API patients from breast cancer studies ignores their heterogeneous health outcomes. To advance cancer health equity among API women, future research should examine inequities within the API population to design interventions that can adequately address their unique differences.