Male breast carcinoma (MBC) accounts for only 1% of total mammary carcinomas. Controversy exists about whether MBC differs clinically and pathologically from female breast carcinoma (FBC). We compared 10 archival cases with 75 stage-matched FBCs. Clinical data, histologic details, immunostains for mammary lineage markers, and results of several putative "prognostic" analyses were addressed, including DNA ploidy and expression of c-erbB-2 (neu) oncoprotein and p53 protein. Cumulative literature data on 2,530 MBCs were contrasted with information from 135 institutional cases of FBC. A statistically significant difference in grade 3 lesions at low stage persisted when MBCs of all stages were compared with similar FBCs. For stages I and IIA, 5-year survival was 60% and 86% for MBCs and FBCs, respectively (also statistically significant). This difference disappeared when all stages were compared. A similar number of MBCs and FBCs, regardless of stage, demonstrated DNA aneuploidy with or without synthesis of S-100 protein, gross cystic disease fluid protein-15, c-erbB-2 protein, and p53 protein. Hormone receptor positivity was more common in MBC than in FBC at high tumor stages. Low-stage MBC and FBC differ biologically; MBCs tend to manifest at a higher grade with lessened 5-year survival. However, aside from distinctions in hormone receptor proteins, broader comparison of MBC and FBC at stages IIB and higher shows no significant differences in 5-year survival or expression of breast cancer-associated gene products.