Because older ages of both mothers and fathers have been hypothesized by others to increase the subsequent risk of breast cancer in female babies, we analyzed the association between maternal and paternal age at birth and mortality from breast cancer in a cohort of 384,796 American women. Cox proportional hazards modeling accounted for age, family history of breast cancer in first-degree relatives, age at menarche, age at first pregnancy, and parity. We found little association between paternal age at birth and death from breast cancer. Although there was no clear linear trend for higher risk with increasing age of the mothers at birth, women born to mothers age 45 years or older had a relative hazard of 1.30 (95% confidence interval = 0.85-1.98), compared with women born to mothers under the age of 20 years. Although these findings are of little public health significance, they may indicate a hormonal profile in older mothers that predisposes female offspring to a higher risk of breast cancer in later years.
