Methods. The distribution of risk factors, which included a family history of breast cancer, age at onset of breast cancer, laterality, race, age at menarche, age at menopause, history of benign breast disease, parity, number of livebirths and number of stillbirths, and age at first childbirth, were examined by histologic subgroup. To determine whether histology is associated with familial risk of breast cancer, a Cox proportional hazards model was used, modeling time to onset of breast cancer among mothers and sisters.

Results. Cases with medullary carcinoma were found to be significantly younger than cases with other tumor types in these data. In addition, medullary carcinoma was reported more frequently among black cases than among white cases. Cases with lobular carcinoma in situ were significantly more likely to have a mother and/or sister affected with breast cancer than cases with other tumor types and were also more likely to be bilateral, although few of these cases were both bilateral and reported a family history of breast cancer. The highest reported rates of benign breast disease occurred in cases with carcinoma in situ (both ductal and lobular) and tubular carcinoma. The remaining risk factors showed no association with histology.

Conclusions. The current study clarifies the extent and nature of the relationship between breast cancer histology and epidemiologic risk factors including a family history of breast cancer.