Familial associations of male breast cancer with other cancers.

PURPOSE: Male breast cancer is associated with female breast cancer in families but whether male breast cancer clusters with other discordant cancers has not been studied. As concordant male breast cancers are utterly rare, discordant associations of male breast cancer with other cancers may reveal genetic and possible environmental risk factors contributing to male breast cancer susceptibility.

METHODS: We calculated relative risks (RRs) for male breast cancer in families with discordant cancers, and conversely, for discordant cancers in families of male breast cancer patients, based on 15.7 million individuals in the Swedish Family-Cancer Database.

RESULTS: Among 1428 male breast cancer patients, 16.2% had a female relative diagnosed with breast cancer. Ovarian and female anal cancers showed the strongest associations with male breast cancer (p value < 0.0005). The other significant associations included colorectal, small intestinal, and thyroid cancers, cancer of unknown primary and non-Hodgkin lymphoma but these were each based on a single positive association with male breast cancer. The RRs for male breast cancer were increased in families in which multiple patients were diagnosed with diverse cancers, reaching an RR of 2.58 when three or more family members were affected.

CONCLUSIONS: The results suggest that male breast cancer shares susceptibility with a number of other cancers but confirmation is needed in other datasets.