Merkel cell carcinoma in Taiwan: A rare tumour with a better prognosis in those harbouring Merkel cell polyomavirus.

Merkel cell carcinoma (MCC) is a rare malignant cutaneous neuroendocrine tumour affecting mainly elderly patients and is more common in the West than in Asia. It is associated with Merkel cell polyomavirus (MCPyV), immunosuppression, and ultraviolet light. In this study, we retrospectively investigated the first series of MCC from Taiwan and identified 19 cases from three tertiary centres. All patients were males with a median age of 67.5. Twelve (63%) cases occurred in the extremities, with one unique case presenting initially as nodal metastasis of unknown primary. Immunohistochemically, the great majority of tumours expressed CK20 (89%), synaptophysin (89%), and INSM1 (84%), with none positive for TTF1. Eleven (58%) cases were positive for MCPyV by immunohistochemistry (clone CM2B4). All patients were treated with excision, including four with additional radiotherapy and one with radiotherapy and chemotherapy. Nodal status and treatment modalities significantly affected survival. The median survival time of MCPyV-positive cases was much longer than the negative cases (median 40 vs. 10 months). In summary, we presented the first report on the clinicopathological features of MCC in Taiwan, with 58% cases associated with MCPyV. The prognosis of patients with MCPyV-positive tumours was better than those negative for MCPyV.