Abstract C046: Second primary cancer risks among Asian American, Native Hawaiian, and other Pacific Islander breast cancer survivors in the United States by race and ethnogeographic region

Abstract Background: Second primary cancer (SPC) risk differs by race and ethnicity among breast cancer survivors, yet Asian American (AA), Native Hawaiian, and other Pacific Islander (NHPI) women are often aggregated into a singular group despite being distinct races with varying cancer burden. Evaluation of SPC risk among breast cancer survivors disaggregated by race (AA, NHPI) and ethnogeographic region (East AA, South AA, Southeast AA) is needed. Methods: We identified 55,028 AA and 5,455 NHPI women diagnosed with a first local/regional unilateral breast cancer between 2000-2019 (followed through 2020) and survived ≥1 year in the Surveillance, Epidemiology, and End Results (SEER) database. SPC was defined as an invasive primary cancer diagnosed ≥12 months after the first primary breast cancer and grouped as 1) all second primary cancer sites combined (excluding ipsilateral breast), 2) all second primary non-breast cancer sites combined, and 3) site-specific second cancers. Risk of SPC was examined by race and ethnogeographic regions categorized as East AA (Chinese, Japanese, Korean), South AA (Asian Indian, Pakistani), Southeast AA (Filipina, Hmong, Kampuchean, Laotian, Thai, Vietnamese), and NHPI (Micronesian including Chamoru and Guamanian; Melanesian including New Guinean, Fijian; Polynesian including Native Hawaiian, Tongan, Sāmoan, Tahitian). We used a competing risk approach for cumulative incidence and subdistribution hazard ratios (SHRs) adjusted for age, year, and clinical characteristics of the index breast cancer (stage, histology, estrogen receptor status, radiation, and chemotherapy). Results: Over a median follow-up of 6.13 years, 3,813 AA women (East AA=1,922, South AA=312, Southeast AA=1,579) and 498 NHPI women developed a SPC. Overall, NHPI women had an increased risk of developing a SPC compared with East AA women (SHR=1.33, 95%CI=1.21-1.47), which was largely driven by a higher risk of contralateral breast, uterine, and ovarian cancer. While South AA women had a lower risk of overall SPC (SHR=0.85, 95%CI=0.75-0.95) compared with East AA women, this was driven by a decreased risk for lung/bronchus (SHR=0.50, 95%CI=0.32-0.80) and colorectal cancer (SHR=0.36, 95%CI=0.21-0.62). Risk of SPC was similar among Southeast AA women compared with East AA women (SHR=0.99, 95%CI=0.93-1.06), but Southeast AA women had a lower risk of digestive system cancer (SHR=0.76, 95%CI=0.65-0.88), and higher risk of uterine (SHR=1.29, 95%CI=1.02-1.63) and thyroid cancer (SHR=1.97, 95%CI=1.47-2.65). NHPI breast cancer survivors had the highest absolute burden of SPC risk with approximately 1 in 10 NHPI women developing a SPC within 10-years of the index breast cancer (10-year cumulative incidence: 7.66% for East AA, 6.25% for South AA, 7.26% for Southeast AA women). Conclusion: Second cancer risks differed between AA and NHPI breast cancer survivors with the greatest risks among NHPI women. Future research is needed to identify factors associated with higher second cancer risks and tailored interventions to promote health equity. Citation Format: Cody Ramin, Jessica P Li, Kekoa Taparra, Geetanjali D Datta, Lene HS Veiga, Gretchen L Gierach, Robert Haile, Amy Berrington de Gonzalez, Jacqueline B Vo. Second primary cancer risks among Asian American, Native Hawaiian, and other Pacific Islander breast cancer survivors in the United States by race and ethnogeographic region abstract. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C046.