Maternal age at birth and risk of breast cancer in daughters.

Data from a large case-control study of breast cancer were examined to test the hypothesis that maternal age at the birth of female offspring is related to the incidence of breast cancer in daughters. Participants were between the ages of 20 and 54 at the time of the study. Based on results for 2,492 parous women who were newly diagnosed with breast cancer and 2,687 parous controls from the general population, a 15-year increase in maternal age was found to be associated with a 29% increase in the risk of breast cancer in daughters. Adjustment for the daughter's age, her own reproductive history, and other potential confounding factors yielded an estimate of 25% for this increase in risk (95% CI, 8% to 46%). The corresponding increase among 499 nulliparous cases and 457 nulliparous controls was 7%, which was not statistically significantly different in magnitude from the increase among parous women. These findings provide evidence for perinatal influences on the subsequent incidence of breast cancer during adulthood. Although specific mechanisms cannot be inferred directly, the results are consistent with the hypothesis that mutations in the genes of the human egg or sperm play a role in the etiology of breast cancer in female offspring.