Migration history, acculturation, and breast cancer risk in Hispanic women

Background: Migrant studies have shown that breast cancer risk increases in women who move from countries with low incidence rates to countries with high rates. We examined the influence of migration history and acculturation on breast cancer risk in Hispanic women ages 35 to 79 years. Methods: In a population-based case-control study conducted in the San Francisco Bay Area, information on migration history, language usage, and other risk factors for breast cancer was collected through an in-person interview for 991 cases and 1,285 controls. Results: Breast cancer risk was 50% lower in foreign-born Hispanics than U.S.-born Hispanics. Risk increased with increasing duration of residence in the United States, decreasing age at migration, and increasing acculturation. Among long-term foreign-born residents, risk was lower among Hispanics who moved to the United States at age >= 20 years and those who spoke mostly Spanish. The difference in risk between third-generation or higher-generation Hispanics and recent migrants from rural areas was similar to 6-fold in postmenopausal women and 4-fold in premenopausal women. Adjustment for differences in the distribution of breast cancer risk factors greatly attenuated the associations with migration patterns in premenopausal women; reduced risks remained only in those who resided in the United States for < 10 years or migrated at age >= 30 years. In postmenopausal women, a 25% to 30% lower risk remained among long-term residents and those who migrated to the United States before age 20 years. Conclusions: These findings suggest the importance of yet unidentified protective factors among both recent premenopausal migrants and postmenopausal migrants.