Male breast cancer in the hereditary nonpolyposis colorectal cancer syndrome

A male member of a large HNPCC kindred, affected by primary malignancies of the breast and colon, was identified. This individual was found to harbor a germline mutation of the MLH1 mismatch repair gene previously shown to se gregate with disease in this kindred. The breast tumor exhibited somatic re duction to homozygosity for the MLH1 mutation, and microsatellite instabili ty was evident in the breast tumor. We conclude that hereditary male breast cancer can occur as an integral tumor in the HNPCC syndrome.