Changes in Breast Cancer Risk and Risk Factor Profiles among US-Born and Immigrant Asian American Women Residing in the San Francisco Bay Area

Background: Breast cancer incidence rates in women of Asian descent have been increasing in the United States and Asia.Methods: In a case-control study of Asian American women from the San Francisco Bay Area, we assessed associations with birthplace and migration-related characteristics and compared risk factors between Asian American and non-Hispanic White women by birthplace and birth cohort.Results: Birthplace and migration-related characteristics were associated with breast cancer risk only among women in the younger birth cohort (1951-1984) that comprised 355 cases diagnosed at age <= 55 years and 276 sister and population controls. Breast cancer risk was marginally increased among foreign-born women [OR = 1.40; 95% confidence interval (CI), 0.97-2.03] and two-fold among foreign-born Chinese women (OR = 2.16; 95% CI, 1.21-3.88). Two-fold increased risks were associated with migration at age >= 40 years and longer U.S. residence (>= 30 years or >= 75% of life). The education level was high among both cases and controls. Differences in the preva-lence of risk factors by birthplace and birth cohort suggest temporal changes in reproductive and lifestyle-related factors. The prevalence in risk factors was similar between foreign-born and U.S.-born women in the younger birth cohort, and did not fully explain the observed associations with birthplace and other migration characteristics.Conclusions: In contrast to studies from earlier decades, younger foreign-born Asian American women had a higher risk of breast cancer than U.S.-born Asian American women.Impact: It is important and urgent to understand what factors drive the increasing burden of breast cancer in women of Asian descent and implement effective prevention programs.

Automated summary

A case-control study in the San Francisco Bay Area found that migration and birthplace are associated with breast cancer risk in Asian American women. Among the younger birth cohort, foreign-born Chinese women had a two-fold increased risk of breast cancer. Other migration characteristics, such as age of migration and length of U.S. residence, were also associated with increased risk. However, the education level did not fully explain these associations.