The aim of our work was to confirm an immunohistochemical profile of routine markers of epithelial and neuroendocrine differentiation in eleven cases of Merkel cell carcinoma, as well as to study the expression of two markers of early phases of neuronal differentiation, namely reelin and class III beta-tubulin, markers which have not yet been studied in Merkel cell carcinomas. In all the investigated tumours the characteristic "dot-like" pattern of cytokeratin 20 immunoexpression, as well as negative immunostaining for cytokeratin 7 and thyroid transcription factor 1 (TTF-1) were disclosed; all the tumours showed neuroendocrine differentiation, expressing either neuron specific enolase (NSE) or chromogranin A(CgA), or both. An interesting finding was observed when the anti-cytokeratin monoclonal antibody MNF 116 was used. The characteristic "dot-like" pattern was detected in high proportion of tumours, including two samples of local recurrence of one of the carcinomas, where neoplastic cells have lost the expression of cytokeratin 20. The majority (91%) of Merkel cell carcinomas included in our group showed positive immunodetection of class III beta-tubulin when TU-20 antibody was used, while TuJ-1 immunostaining was surprisingly negative in all the investigated tumours. Detection of reelin was negative in almost all the studied Merkel cell carcinomas except for cases, where neoplastic cells revealed weak focal immunostaining in a minor portion of neoplastic cells.

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