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Distinguishing primary adnexal tumors from skin metastases with visceral origins can be a diagnostic challenge. These authors performed a retrospective analysis of 113 cases (59 primary adnexal carcinomas and 54 cutaneous metastases) to explore the role of immunohistochemical staining in elucidating this diagnostic dilemma.
The primary adnexal carcinomas included apocrine, eccrine, mucinous, and trichilemmal carcinomas, porocarcinoma, hidradenocarcinoma, microcystic adnexal carcinoma, and adenoid cystic carcinoma. The metastases originated from primary tumors of the breast, lung, ovary, endometrium, gastrointestinal system, and kidney. Immunohistochemical stains for p63, cytokeratin (CK) 15, calretinin, D2-40, and nestin were performed and scored by the percentage of positive cells. Staining showed p63 in nearly all of the adnexal neoplasms, except apocrine and mucinous carcinomas. D2-40, CK15, and nestin were expressed in 44%, 40%, and 37% of the adnexal neoplasms, respectively, but calretinin expression was noted in only 14%. The markers p63, CK15, nestin, and D2-40 had statistical significance for distinguishing primary adnexal carcinoma from cutaneous metastasis. In a logistic regression analysis, p63, CK15, and D2-40 but not nestin retained significance in identifying a primary adnexal carcinoma.
Mahalingam M et al. The diagnostic utility of immunohistochemistry in distinguishing primary skin adnexal carcinomas from metastatic adenocarcinoma to skin: An immunohistochemical reappraisal using cytokeratin 15, nestin, p63, D2-40, and calretinin. Mod Pathol 2010 May; 23:713.
Comment
Metastases to the skin occur in 10% of visceral neoplasms. They can indicate advanced tumor stage, failed treatment, or an occult malignancy. Although papules and nodules represent the classical clinical appearance of a metastasis, the clinical presentation can vary widely. Therefore, immunohistochemical stains are useful for differentiating metastases from primary adnexal neoplasms. As the authors suggest, sensitivity and specificity can be improved by using a diagnostic panel of p63, CK15, and D2-40. A tumor with positive staining to all three markers is likely to be a primary cutaneous adnexal neoplasm.