Age of mother and grandmother in relation to a subject's breast cancer risk

BACKGROUND: On theoretical grounds, the age of the grandmother and the age of the mother at delivery of her daughter may affect the breast cancer risk of the granddaughter. METHODS: We used the data relating to the Diagnostic Research Mamma-carcinoma cohort (DOM (Diagnostisch Onderzoek Mammacarcinoom) 3), which comprises a population-based sample of 12 178 women aged 41–63 years at enrolment in 1982–85 and followed up until 2000. During follow-up 340 postmenopausal breast cancer cases were identified. To these we applied a case–cohort design together with a random sample from the baseline cohort (n=1826). Of these study participants, we were able to retrieve the birth dates of 998 mothers (309 cases, 689 controls), and for 547 of these we also retrieved the birth dates of the grandmothers (197 cases, 350 controls). A weighted Cox proportional hazards model was used to estimate the hazard ratios (HRs) for the effect of the age of the grandmother and the age of the mother on the breast cancer risk of the index women, while adjusting for potential confounders. RESULTS: Compared with the reference group aged 25–29.9 years, the group with the lowest maternal age (<25 years) had an age-adjusted HR of 0.77 (95% CI 0.19–3.12) and the group with the highest maternal age (⩾40 years) had an age-adjusted HR of 1.58 (95% CI 0.01–267.81), P-value for trend=0.62. Compared with the same reference group, the group with the lowest grandmaternal age (<25 years) had an age-adjusted HR of 0.53 (95% CI 0.24–1.17) and the group with the highest grandmaternal age (⩾40 years) had an age-adjusted HR of 7.29 (95% CI 1.20–44.46), P for trend=0.04. The associations did not change significantly after additional adjustment for various risk factors for breast cancer, neither for maternal age nor for grandmaternal age. CONCLUSION: This study does not suggest a major role of maternal age at delivery or grandmaternal age at delivery of the mother for the (grand)daughters' breast cancer risk.