Although CK20was negative, the NEC exhibited an immunophenotype suggestive of a Merkel cell carcinoma with diffuse positive staining with FLI-1, SATB2 and neurofilament, markers which are preferentially expressed in Merkel cell carcinoma compared with other NECs.
The diagnostic accuracy of each marker was then assessed in a validation set of 103 Merkel cell carcinomas (9 CK20-negative cases and 15 cases without a primary skin tumor) and 70 extracutaneous neuroendocrine carcinoma cases.
The importance of distinguishing metastatic neuroendocrine carcinoma (NEC) from primary neuroendocrine carcinoma in the skin, or Merkel cell carcinoma (MCC), has been stressed in the literature, with CK20 positivity traditionally being reported as the key diagnostic feature of MCC.
Herein, we studied 10 combined cutaneous squamous cell and neuroendocrine carcinomas for immunohistochemical expression of p53, retinoblastoma 1 protein, neurofilament, p63, and cytokeratin 20 (CK20).
CK20 and neurofilament positivity in some cervical neuroendocrine carcinomas is in keeping with a Merkel cell immunophenotype, similar to that described in SCNECs in other organs.