Objective: Women with a strong family history of breast cancer are at significantly increased risk of developing the disease. There is emerging evidence that certain reproductive factors may further elevate risk in these women. We examined whether a family history of breast cancer modifies the association between correlates of endogenous hormonal exposures and breast cancer in a study of 426 families ascertained through breast cancer probands.
Methods: Analyses of reproductive factors and breast cancer were performed on 395 sisters and daughters of probands, 3014 nieces and granddaughters. and 2768 marry-ins.
Results: Through 226,266 person-years of follow-up since 1952, 240 women developed breast cancer. No statistically significant interactions were observed between relationship to proband and age at menarche, age at menopause, other characteristics of the menstrual cycle, parity, age at first and last birth, infertility, and total ovulatory years.
Conclusions: Our findings suggest that most reproductive factors influence breast cancer risk similarly in women with and without a family history of breast cancer. Further studies are needed on individuals who are more homogeneous with regard to hereditary background. However, other options for prevention, such as prophylactic surgery or chemoprevention, may be necessary to have a substantial impact on risk reduction in women at high genetic risk.