Cutaneous metastases of pancreatic neuroendocrine carcinoma.

Neuroendocrine carcinomas with distant metastases are rarely reported in the literature, with cutaneous metastases being among the most infrequently reported sites. 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. Our case not only serves as one of the few reported cases of cutaneous metastases of a visceral NEC, but also serves to caution providers as to the use of CK20 positivity as an absolute diagnostic feature. We present a case of a 67-year-old female with widespread cutaneous metastases of a pancreatic NEC. Immunohistochemical staining revealed CK20 positivity, despite visceral origin of the primary tumor. This case serves to highlight not only a rare presentation of cutaneous metastases of a pancreatic neuroendocrine carcinoma, which has yet to be reported in the literature, but also serves as the only report of a pancreatic NEC with CK20 positivity, providing evidence for cautionary use of CK20 staining for diagnostic purposes, particularly for visceral NECs which have been under-represented in the literature.