Presence of the Merkel cell polyomavirus in Merkel cell carcinoma combined with squamous cell carcinoma in a patient with chronic arsenism.

We present a case of Merkel cell carcinoma (MCC) coincident with squamous cell carcinoma (SCC) on the breast of a woman with chronic arsenism. This case demonstrates the distinct association of chronic arsenism with two different primary cutaneous carcinomas. Merkel cell polyomavirus (MCPyV) was identified in the lesional skin of the MCC but not in that of the SCC, suggesting there are different interactions of MCPyV in the pathogenesis of SCC and MCC related to arsenic. Physicians need to be vigilant in the occurrence of both SCC and MCC in patients with chronic arsenism. To our knowledge, this is the first study to show the presence of MCPyV in the MCC but not the SCC portion of an arsenic-induced tumour.