Introduction: Diabetes during pregnancy is related to enhanced fetal growth, which has been associated with increased breast cancer risk. Whether daughters of mothers with a diagnosis of diabetes have an increased risk of breast cancer is not known.
Methods: We performed a retrospective cohort study of daughters of mothers with diabetes by linkage of the Swedish Multigeneration, Cause-of-Death and Patient Register between 1952 and 2005. Breast cancer cases were ascertained by linkage with the Swedish Cancer Register between 1958 and 2005. Standardized incidence ratios (SIRs) of breast cancer were calculated assuming a Poisson distribution for the observed cases.
Results: We identified 291,360 daughters of mothers with a diagnosis of diabetes before or after birth between 1952 and 2005. Among the daughters, 7,956 cases of breast cancer were diagnosed between 1964 and 2005. The total time of follow-up was 12,173,821 person years. The expected number of breast cancer cases was 9,204, resulting in an SIR of 0.86 (95% CI, 0.85 to 0.88). The decrease in risk associated with maternal diabetes was stronger for premenopausal (< 55 years of age) than postmenopausal (> or = 55 years of age) breast cancer (SIR 0.83 and 0.91, respectively). Among daughters of mothers with diabetes, a history of breast cancer in the mother increased the risk of breast cancer in the daughter (SIR 1.43, 1.32 to 1.54).
Conclusions: Daughters of mothers with a lifetime history of diabetes were at a decreased risk of breast cancer. The strongest negative association was found among premenopausal breast cancer.