BerEP4 positivity in Merkel cell carcinoma: a potential diagnosis pitfall.

Merkel cell carcinoma (MCC) is a primary neuroendocrine carcinoma of the skin with a 5-year overall survival estimated at 40%.1 In 2008, Merkel cell polyomavirus (MCPyV) integration was identified as the primary oncogenic event of about 80% of MCC cases.1 Under microscopic examination, MCC appears as a proliferation of basaloid tumour cells invading the dermis and subcutaneous tissues.2 Accordingly, MCC belongs to the spectrum of small, round and blue cell proliferations, and differential diagnosis includes haematological malignancies (acute leukaemia and chronic lymphocytic leukaemia), sarcomas and small cell variants of melanoma. Interestingly, positivity of BerEP4 in MCC tumour cells was recently emphasized in the new WHO classification of skin tumours,2 suggesting BerEP4 positivity as a potential pitfall in distinguishing BCC and MCC. Although MCC tumour cells harbour specific cytological features,3 some specimens might be misdiagnosed as BCC especially on small-size biopsies.3 In this specific context, positivity of BerEP4 might constitute a potential diagnostic pitfall. [Extracted from the article]