Abstract PO5-08-12: Ethnic Admixture Affects Breast Cancer Incidence in Native Hawaiians: The Multiethnic Cohort

Abstract Background Native Hawaiians (NH) have the highest breast cancer incidence and the poorest survival of any ethnic group in Hawaii [1]. Since it has been shown that different ethnic groups have disparate risk of breast cancer in Hawaii and NHs are commonly of mixed ancestry, it is possible that the specific ethnic admixture may present an altered risk profile. For example, NH with Asian admixture was associated with higher risk for type 2 diabetes independent of known risk factors [2] compared to those without. The objective of this study was to calculate crude and age-adjusted breast cancer incidences by ethnic admixture group among participants of the Multiethnic Cohort (MEC). Methods: Based on self-reports, 106,525 eligible women were categorized by broad ethnic categories: Native Hawaiian, White, Black, Latino, and Japanese. In total there were 9257 breast cancer cases in the MEC cohort (1996-2019) at time of analysis. The Native Hawaiian population was further categorized into the following subgroups: Native Hawaiian only, Native Hawaiian & White, Native Hawaiian & Chinese, Native Hawaiian & White & Chinese. Crude and age-adjusted incidence rates (per 1000 person-years) were calculated for the various groups. The direct method of age adjustment using the US 2000 Standard population was used. Results: The ethnicity with the highest crude incidence were White=88.46, followed by Black=85.20, Latino=84.27, Japanese=84.90, and Native Hawaiian=81.28. However, after age-adjustment the highest were Japanese=159.1, White=153.8, Latino=148.3, Black=147.4, and Native Hawaiian=139.1. Crude incidence rates for Native Hawaiian ethnic admixture was found to be highest for Native Hawaiian & White=83.5, Native Hawaiian only=82.5, Native Hawaiian & Chinese=80.8, and Native Hawaiian & White & Chinese=80.4. After age adjustment, the highest was Native Hawaiian & Chinese=173.9, followed by Native Hawaiian & White=154.3, Native Hawaiian only=148.7, and finally Native Hawaiian & White & Chinese=120.8. Conclusion: These findings indicate that ethnic admixture in Native Hawaiians may be at elevated age-adjusted breast cancer incidence when compared to Native Hawaiian alone. When a woman was Native Hawaiian and Chinese the incidence was notably higher than any other group at 173.9 when compared to all Native Hawaiian=139.1. Furthermore, the group that had the lowest age-adjusted incidence was the mixed group of Native Hawaiian & White & Chinese=120.8 which seems to account for why the overall Native Hawaiian group=139.1 had one of the lowest incidence rates of the 5 major ethnic groups. 1. Loo, L.W., M. Williams, and B.Y. Hernandez, The high and heterogeneous burden of breast cancer in Hawaii: A unique multiethnic US Population. Cancer epidemiology, 2019. 58: p. 71-76. 2. Maskarinec, G., et al., Ethnic admixture affects diabetes risk in native Hawaiians: the Multiethnic Cohort. Eur J Clin Nutr, 2016. 70(9): p. 1022-7. Citation Format: Dustin Valdez, Arianna Bunnell, David Bogumil, Gertraud Maskarinec, John Shepherd. Ethnic Admixture Affects Breast Cancer Incidence in Native Hawaiians: The Multiethnic Cohort [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-08-12.