Cytokeratin 20: A marker for diagnosing Merkel cell carcinoma

Merkel cell carcinoma is an aggressive cutaneous neoplasm that is often dif ficult to diagnose because of its histologic and immunohistochemical simila rity to metastatic oat cell carcinomas and other cutaneous neoplasms. Our p urpose was to determine the utility of immunoperoxidase staining of cytoker atin 20 (CK 20) a newly discovered intermediate filament protein, in Merkel cell carcinomas and other cutaneous tumors. Sixty-one tumors were sectione d and stained with antibodies directed at CK 20. The staining of Merkel cel l carcinomas was compared with metastatic oat cell carcinomas, lymphomas, s quamous cell carcinomas, basal cell carcinomas, melanomas, metastatic carci noids. spiradenomas, eccrine carcinomas, adenoidcystic carcinoma, sebaceous carcinomas, hidradenomas, sebaceous epitheliomas. trichoblastomas, mixed t umors, and metastatic adenocarcinomas. Nine of 10 Merkel cell carcinomas st ained with antibody to CK 20. Two metastatic carcinomas to the skin were al so positive. One hidradenoma and one squamous carcinoma exhibited focal sta ining, but were otherwise negative. All other turners were nonstaining. Cyt okeratin 20 is a sensitive and specific marker for Merkel cell carcinoma an d is helpful in distinguishing between Merkel cell carcinoma and other mali gnant and benign neoplasms.