The frequency, distribution, and morphologic spectrum of the various histologic subtypes of male breast cancer as compared with its female counterpart may provide a valuable insight into the etiology and/or pathogenesis of both. This was perhaps best illustrated in the study of ductal carcinoma in situ by Hittmair et al. [13
]. The authors showed that in the male breast, papillary DCIS occurred with a much higher frequency (46% of pure lesions) than expected, while solid, micropapillary, and cribriform patterns occurred with a much lower frequency (22% of pure DCIS combined). Notably, only 5 of 114 cases were of comedo-type DCIS and only 7 of 114 cases were considered high grade. The authors concluded that predominance of papillary patterns among intraepithelial male breast lesions is a reflection of the relative abundance of ducts and the poorly developed terminal-ductal lobular units in male breast. Given the rarity of true comedo DIN in male breast, the authors speculated that the fully developed lobular environment and the female type hormonal milieu may be a requirement for development of comedo DIN [13
In this study, we investigated in detail 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 findings suggest that invasive carcinoma of the male breast displays a morphologic spectrum and distribution of histologic subtypes that is comparable to invasive carcinoma of the female breast and that no specific histologic subtypes are notably over- or underrepresented with the exception of papillary and lobular variants.
Papillary intraductal carcinomas basically assumed an infiltrating duct carcinoma pattern once they invaded the stroma (Fig. e,f). A papillary component was present in 34 (4.5%) of 759 cases, representing the second most common histologic subtype. These papillary carcinomas appeared to have invaded either through massive expansion and total disruption of ductal confines with typical invasive patterns at their periphery or only focally disrupted the duct wall and invaded the surrounding stroma as an infiltrating duct carcinoma. The latter represents approximately 2% [5
] of female breast invasive carcinomas and appears overrepresented in males. In a large population-based study, Giordano et al. [7
] reported that 2.6% of invasive malignancies in males were papillary carcinomas, as compared with 0.6% in females (p
0.0001). However, the differences between males and females with respect to the frequencies of the other histologic subtypes were also statistically significant. The significance of the papillary histologic subtype or papillary architecture in male ductal carcinoma requires further investigation but is most probably related to the architecture of the male mammary duct system with dominance of larger ducts.
The possibility of metastases to the breast should be considered when evaluating breast masses particularly if there is a history of cancer elsewhere. Nineteen cases of carcinoma metastatic to the male breast were seen over this study period, representing 2.4% (19/778) of all nonhematopoietic or lymphoreticular malignancies. This is again a twofold increase comparable to the 1.2% reported in female breast malignancies over a 10-year period [11
]. Of the 19 metastatic tumors, 58% (11/19) were cutaneous melanomas, and 21% (4/19), 10% (2/19), and 10% (2/19) represented carcinomas from the prostate, lung, and larynx, respectively. It is interesting to note that prostatic carcinoma, which has been the subject of most reports of carcinomas metastatic to the male breast [10
], was not the most common metastatic tumor in this series. The number of metastatic tumors in this series is relatively small, which is a limitation in interpreting the distribution of originating sites. Nonetheless, in the investigation of metastatic tumors to the male breast of an unknown primary site, our findings provide additional data on some of the most likely sites.
This study also confirms the occurrence of lobular carcinoma in the male breast. Three cases of invasive lobular carcinoma, diagnosed purely on a morphologic basis, were present among 759 cases (0.4%). Three additional cases of mixed lobular and ductal carcinoma were also diagnosed over this period (0.4%). Joshi et al. [16
] found one (4%) lobular carcinoma out of 27 cases, while Goss et al. [8
] found 4 (1.9%) cases out of a total of 229. In the series of Giordano et al. [7
], lobular carcinomas constituted 1.5% for their male breast cancers. It is noteworthy that all of these cases were interpreted as lobular based on morphology without E-cadherin immunostain confirmation.
In summary, invasive carcinoma of the male breast appears to display a morphologic spectrum and distribution of histologic subtypes, which is comparable to invasive carcinoma of the female breast with some variation. As expected, lobular carcinoma is exceedingly rare but was encountered in this series. There appears to be a twofold increase in the frequency of invasive papillary carcinoma and metastatic cancers to the male breast as compared to published data in the female breast. Finally, the most common tumor metastatic to the male breast in this series was cutaneous melanoma.