Description

Merkel cell carcinoma (MCC) is a rare, aggressive primary cutaneous neoplasm which shows neu-roendocrine differentiation and commonly arises on the head and neck or extremities of the elderly. Its putative origin from,or differentiation t ward, the Merkel cell has been disputed such that there is increasing use of the term primary neuroendocrine carcinoma of the skin.

The difficulty in distinguishing MCC from many potential morphological mimics including peripheral primitive neuroectodermal tumour (PNET), lymphoma, poorly differentiated epidermal and adnexal neoplasms and Merkel-like small cell melanoma has been alleviated in the last decade with the availability f potentially discriminatory antibodies applicable t paraffin-section immunohist chemistry.In contrast, the most difficult and, possibly, important differential diagnosis of metastatic small cell carcinoma (SCC) has remained problematic, relying heavily on the clinical exclusion of a lung or other primary. H wever, several recent reports have suggested that the differential expression of cytokeratin 20 and neurofilaments by MCC and metastatic SCC is of considerable value. This report highlights the diagnostic utility of immunohist chemistry in the definitive pathological diagnosis of MCC.