Risk of familial breast cancer is not increased after pregnancy.

Risk of breast cancer is temporarily elevated shortly after pregnancy and the available limited data suggest that a family history of breast cancer may reinforce the risk. We used the nation-wide Swedish Family-Cancer Database to estimate the relative risk (RR) for invasive breast cancer following childbirth among women with or without a family history. The RRs were defined using Poisson regression model of person-years as offset, adjusted for age, period and age at first childbirth. For women without a family history, RRs for breast cancer showed a U-shaped pattern after last pregnancy. Among the 5,217 patients with a first-degree family history the familial risk was 1.77; there was no evidence of increased RRs immediately after last pregnancy. The present study is by far the largest one published on the theme. It shows that pregnancy is not an additional risk factor for women with a family history.