An Immunohistochemical Panel to Differentiate Metastatic Breast Carcinoma to Skin From Primary Sweat Gland Carcinomas With a Review of the Literature

Context.-Approximately 25% of patients with breast cancer develop cutaneous metastases. Sweat gland carcinomas (SGCs) account for about 0.05% of all cutaneous neoplasms. Cutaneous metastases of breast carcinoma (CMBCs) (especially the ductal type) can be difficult to distinguish from SGCs. Treatment and prognoses for these 2 types of tumors differ radically, making accurate histologic diagnosis crucial. Although a few studies attempt to differentiate these entities employing immunohistochemical (IHC) studies (some of which we review here), to date, no panel of IHC stains exists, to our knowledge, to distinguish these entities. Objective.-To devise a panel of IHC stains to distinguish CMBC from SGC. Design.-Twelve cases of ductal CMBCs (11 not otherwise specified type, and 1 basal phenotype), 11 cases of SGCs (5 eccrine carcinomas, 3 porocarcinomas, and 3 microcystic adnexal carcinomas), 2 benign sweat gland neoplasm cases, and 2 primary breast cancer cases were retrieved and analyzed with the following IHC panel: mammaglobin, gross cystic disease fluid protein (GCDFP) 15, p63, basal cytokeratins (CK5, CK14, and CK17), androgen receptor, and PAX5. Results.-The p63 was only weakly expressed in 1 of 12 CMBC cases (8.3%), whereas it was strongly expressed in 10 of 11 SGC cases (90.9%) (P<.001). Basal cytokeratins demonstrated a similar immunoprofile in the SGC group, with 10 of 11 cases (90.9%) expressing all 3 markers, and a variable immunoprofile in the CMBC group with 0% (CK14) (P<.001) to 16.7% (2 of 12 cases; CK5 and CK17) (P<.001) expression. Mammaglobin was expressed in 8 of 12 cases (66.7%) of CMBC. Conclusions.-Together, these 5 IHC stains were combined to make a panel that was 100% sensitive and 91% specific in distinguishing between CMBC and SGC. (Arch Pathol Lab Med. 2011;135:975-983)