We describe herein the clinical characteristics of five male breast carcinoma (MBC) patients with a familial history of breast carcinoma (FHBC). Four of these patients suffered from multiple primary cancers, being gastric and prostate cancer in 1, gastric cancer in 1, and asynchronous bilateral breast cancers in 2. The average age of these patients at diagnosis was not lower than that of MBC patients with no such familial history. The aggregation of cancer in these families had three prominent characteristics: (1) The families included women with early-onset breast cancers which had occurred at the ages of 38, 38, and 35 years, respectively, and/or early-onset uterine cancer which had occurred at the age of 35 years. (2) The incidence of multiple primary cancers was significantly higher in the siblings of MBC patients with a FHBC than without. (3) There were many cancers in hormone-related organs in two families.