Background: Previous studies have provided conflicting results concerning the effects of a family history of prostate and other cancers on breast cancer risks.
Methods: Three groups of families were studied to determine the effects of a family history of prostate cancer on breast cancer risks. Also considered were the effects of a family history of melanoma, colon, lung, ovarian, and endometrial cancers. Included were 422 first-degree female relatives of 114 patients with bilateral breast cancer, 320 first-degree relatives of 88 male patients with breast cancer, and 633 relatives of 186 unselected female patients. For estimating relative risks, observed numbers of breast cancers in relatives were compared with expected numbers based on population incidence data. Multiple logistic-regression also provided odds ratios of relatives affected with breast cancer.
Results: A family history of prostate cancer increased the breast cancer risks in each of the groups, compared with families without prostate cancer. Ovarian cancer in a family increased the breast cancer risks only in the bilateral breast cancer group, and endometrial cancer increased the risks in the bilateral and unselected groups. These increases in risk appeared to be the consequence of families with multiple cancers, including those with hereditary breast-ovarian cancers and the cancer family syndrome. A family history of melanoma, lung, or colon cancer did not increase breast cancer risks.
Conclusions: A family history of prostate cancer, as well as endometrial and ovarian cancer, significantly increases the risk of breast cancer.