Differentiating cutaneous metastases of breast carcinoma from sweat gland carcinomas

  Approximately 25 percent of patients with breast cancer develop cutaneous metastases. Sweat gland carcinomas (SGCs) account for about 0.05 percent of all cutaneous neoplasms. Cutaneous metastases of breast carcinoma (CMBC), especially the ductal type, can be difficult to distinguish from SGCs. Treatment and prognoses for these two types of tumors differ radically, making accurate histologic diagnosis crucial. Although a few studies attempt to differentiate these entities employing immunohistochemical (IHC) studies, the authors know of no panel of IHC stains to distinguish these entities. Therefore, the authors sought to devise a panel of IHC stains to distinguish CMBC from SGC. They retrieved from the University of Pittsburgh Medical Center archives 12 cases of ductal CMBCs (11 not otherwise specified type and one basal phenotype), 11 cases of SGCs (five eccrine carcinomas, three porocarcinomas, and three microcystic adnexal carcinomas), two benign sweat gland neoplasm cases, and two primary breast cancer cases. The authors then analyzed these cases with the following IHC panel: mammaglobin, gross cystic disease fluid protein (GCDFP) 15, p63, basal cytokeratins (CK5, CK14, and CK17), androgen receptor, and PAX5. The authors found that p63 was only weakly expressed in one of 12 CMBC cases (8.3 percent), whereas it was strongly expressed in 10 of 11 SGC cases (90.9 percent; P<.001). Basal cytokeratins demonstrated a similar immunoprofile in the SGC group, with 10 of 11 cases (90.9 percent) expressing all three markers, and a variable immunoprofile in the CMBC group, with zero (CK14; P<.001) to 16.7 percent (two of 12 cases; CK5 and CK17; P<.001) expression. Mammaglobin was expressed in eight of 12 cases (66.7 percent) of CMBC. The authors concluded that together, mammaglobin, p63, and the three basal cytokeratins combined made a panel that was 100 percent sensitive and 91 percent specific in distinguishing between CMBC and SGC.