Merkel cell carcinoma with cytokeratin 20-negative and thyroid transcription factor-1-positive immunostaining admixed with squamous cell carcinoma.

摘要

Merkel cell carcinoma (MCC) is an aggressive cutaneous tumor with a rapidly increasing incidence. Merkel cell polyomavirus (MCPyV) is a recently identified virus that may be involved in the oncogenesis of MCC [1]. The diagnosis of MCC requires immunohistochemical markers. Distinguishing primary MCC from small cell carcinoma of the lung (SCCL) is a critical issue. Most MCC stain positive for cytokeratin 20 (CK20) and negative for thyroid transcription factor-1 (TTF-1). MCPyV, identified using polymerase chain reaction (PCR), is a specific marker for MCC that can be helpful for differentiating MCC from SCCL and other neuroendocrine tumors [2]. Here we report a collision tumor comprising a rare variant type of MCC with CK20-negative and CD56/TTF-1-positive immunostaining and invasive SCC.