Parental ages at birth in relation to a daughter's risk of breast cancer among female participants in the Framingham Study (United States).

Data from the Framingham Heart Study, collected in Framingham, MA (United States) during 1948-86, were used to evaluate the relation of parental age at birth to the risk of breast cancer among daughters. After 38 years of follow-up, 149 breast cancer cases occurred among 2,662 women. All but two cases were confirmed by histologic report. The rate of breast cancer increased among daughters with increasing maternal age at birth up to the mid-30s, where the rate levelled off. A similar pattern was observed with paternal age. After adjustment for other confounding factors and paternal age, the rate ratios for breast cancer in daughters whose mothers were aged 26 to 31 years and 32 or more years at their birth, relative to women whose mothers were aged 25 years or younger, were 1.5 (95 percent confidence interval [CI] = 1.0-2.4) and 1.3 (CI = 0.8-2.2), respectively. However, there was no longer an association between paternal age at birth and risk of breast cancer after controlling for maternal age and other risk factors.