Cutaneous metastases of breast carcinoma can be histologically similar to primary skin tumors with eccrine differentiation. We compared the immunohistochemical staining characteristics of 15 metastatic breast carcinoma skin lesions in 12 patients to those of a series of primary eccrine tumors using estrogen receptor, progesterone receptor, and anti-gross cystic disease fluid protein-15 markers. Anti-gross cystic disease fluid protein-15 positivity was noted in 7 of 15 breast carcinoma skin metastases, 0 of 5 benign eccrine tumors, 1 of 6 microcystic adnexal carcinomas, and 1 of 1 metastatic sweat gland adenocarcinoma. Estrogen receptor positivity was found in 1 of 15 metastatic breast carcinoma skin lesions, 0 of 5 benign eccrine tumors, 2 of 8 microcystic adnexal carcinomas, and 1 of 1 metastatic sweat gland adenocarcinoma. Progesterone receptor positivity was identified in 15 of 15 metastatic breast carcinoma skin lesions, 2 of 5 benign eccrine tumors, 5 of 8 microcystic adnexal carcinomas, and 1 of 1 metastatic sweat gland adenocarcinomas. These results indicate that standard immunohistochemical staining for estrogen receptors, progesterone receptors, and gross cystic fluid protein-15 markers will not reliably distinguish primary (or metastatic) eccrine tumors from cutaneous metastases of breast carcinoma.