Reproductive risk factors for breast cancer in Hispanic and non-Hispanic white women: the New Mexico Women's Health Study.

The authors conducted a population-based case-control study of breast cancer in Hispanic women in New Mexico. Hispanic and non-Hispanic white women with incident breast cancer, aged 30-74 years and diagnosed between 1992 and 1994, were identified by the New Mexico Tumor Registry. Controls were selected using random digit dialing and frequency matched by ethnicity, age, and region. Information on reproductive history, lactation, and other risk factors was collected through in-person interviews; 719 Hispanics and 836 non-Hispanic whites were included in the analysis. Conditional logistic regression was used to estimate relative risk of breast cancer for reproductive factors and to assess ethnic differences in effects. Older age at first full-term birth was associated with breast cancer among Hispanics; the odds ratio for women aged 27 years and older at first full-term birth compared with women 18 years or younger was 2.26 (95% confidence interval 1.17-4.38) compared with 1.60 (95% confidence interval 0.86-3.01) for non-Hispanic whites. Higher parity was associated with reduced risk of breast cancer for non-Hispanic whites, but not Hispanics (p < 0.008). Longer lactation was associated with reduced risk in premenopausal Hispanic women and premenopausal and postmenopausal non-Hispanic white women. Reproductive factors explained 17% of the ethnic difference in breast cancer incidence for postmenopausal women and none of the difference for premenopausal women.