Immunohistochemical distinction of primary sweat gland carcinoma and metastatic breast carcinoma: can it always be accomplished reliably?

Even with adequate history, the distinction of cutaneous metastatic breast carcinoma from primary sweat gland carcinoma can be difficult. Although previous studies have attempted to separate these tumors with various immunohistochemical panels, those series have been limited by small numbers of patients as well as the inclusion of benign sweat gland tumors. In this analysis, stains for p63, CK5/6, and D2-40 were included, as well as GATA3 and mammaglobin, in an evaluation of 21 primary sweat gland carcinomas and 33 examples of cutaneous metastatic breast carcinoma. Immunoreactivity for p63, CK5/6, D2-40, GATA3, and mammaglobin was respectively observed in 81%, 71%, 52%, 71%, and 5% of sweat gland carcinomas compared with 6%, 6%, 6%, 91%, and 45% of metastatic breast carcinomas. These differences were statistically significant for p63, CK5/6, and D2-40. For the diagnosis of metastatic breast carcinoma, GATA3 was the most sensitive marker (91%), but its sensitivity was substantially lower. Mammaglobin was 95% specific for breast carcinoma but again suffered from limited sensitivity (45%) in this context. These data suggest that p63 and CK5/6 are specific determinants for sweat gland carcinoma in the stated setting. In the absence of those analytes, metastatic breast carcinoma cannot always be identified to the exclusion of a primary tumor. This diagnostic scenario continues to require the procurement of a detailed clinical history regarding the number and duration of skin lesions in any given case.