Breast cancer in males is relatively uncommon, with approximately 1,450 newly diagnosed cases annually in the United States, and an associated mortality rate that accounts for less than 0.2% of all cancer-related deaths in men [1, 4, 9, 15, 17, 20, 28]. However, recent epidemiologic studies suggest that the incidence of male breast cancer has been steadily increasing [7, 14]. Utilizing data from the National Cancer Institute’s Surveillance, Epidemiology and End Results database for the 26-year period between 1973 and 1998, Giordano et al.  found that the incidence of male breast cancer increased from 0.86 to 1.08 per 100,000 population. This increasing incidence, in addition to the better elucidation of the role of BRCA2 mutations in male breast cancer, has renewed interest in specifically identifying the underlying pathogenesis of male breast cancer and clarifying the specific differences, if any, between male and female breast cancer.
On a broad demographical level, male and female breast cancers are fundamentally similar with the main differences lying in older age of occurrence and lower incidence of the former. However, significant differences have been noted between male and female breast cancers with respect to the expression of a variety of biologic factors, including hormone receptors such as estrogen receptor, progesterone receptor, c-erbB-2, estrogen-inducible proteins such as pS2, Cathepsin D, hsp27, proteins related to basement membrane and extracellular matrix degradation such as the urokinase system of plasminogen activation and their inhibitors, and protooncogenes such as bcl-2 [2, 6, 7, 18, 21, 22, 24, 27]. At the morphologic level, male ductal intraepithelial neoplasia (ductal carcinoma in situ), in contrast to similar lesions in females, displays a distinct histologic profile in which the majority of tumors are of the papillary type, with cribriform, micropapillary, and solid types being much less common . In particular, the comedo-type of DIN (comedo DCIS) is notably rare in the male breast . For invasive carcinomas, the female and male tumors are morphologically indistinguishable  and many published studies on male breast cancer frequently represent the major histologic subtypes of nonlobular breast carcinoma, such as ductal, medullary, mucinous, and papillary [3, 7, 8, 12, 19, 22, 25]. However, these studies generally do not have the distribution and relative frequencies of the various histologic subtypes as their main focus, and as such, pathologically important distinctions such as signet ring vs colloid carcinoma (both subsumed under mucin producing carcinoma), or metaplastic carcinoma vs infiltrating duct carcinoma not otherwise specified are not emphasized. Over- or underepresentation of a particular histologic subtype in male breast cancers may provide valuable insight into the etiopathogenetic differences between male and female breast cancers and may provide an important nidus for further studies.
In this study, we investigated the frequencies and distribution of the various histologic subtypes in a large data set of invasive carcinomas seen at a large tertiary center over a 40-year period. Our goals are to document these frequencies and distribution and to see whether any histologic subtypes are notably distinct in frequency of occurrence in the male breast, as compared with historical published data on similar lesions in the female breast. The frequencies and sites of origin of metastatic tumors to the male breast during the study period were also investigated.