Lack of evidence for basal or squamous cell carcinoma infection with Merkel cell polyomavirus in immunocompetent patients with Merkel cell carcinoma.

BACKGROUND Merkel cell polyomavirus (MCV) was discovered by digital transcriptome subtraction as a monoclonal infection of Merkel cell carcinoma (MCC) tumors. Subsequent studies have repeatedly confirmed that MCV is the likely cause for most MCC. Polymerase chain reaction-based detection of the virus in other nonmelanoma skin cancers, however, has been inconsistent and controversial. OBJECTIVE We sought to directly assay for MCV infection in squamous cell carcinoma (SCC) or basal cell carcinoma (BCC) tumor cells by immunostaining for viral antigen. METHODS CM2B4, a monoclonal antibody to exon 2 peptides of MCV T antigen, was used to examine tumors from 20 patients with MCC with and without secondary SCC or BCC tumors. RESULTS MCV T antigen was readily detected in 15 (75%) of 20 MCC tumors including 11 MCC tumors from patients with secondary SCC or BCC. In contrast to MCC, none of these secondary BCC or SCC was MCV T-antigen positive. LIMITATIONS A limitation was the small study size with antigen detection including only the MCV large T and 57kT proteins. CONCLUSIONS MCV T antigen is generally not expressed in BCC or SCC tumors from a population favored to have MCV infection, ie, those persons already given the diagnosis of MCV-positive MCC. This suggests that episodic polymerase chain reaction detection of MCV genome in BCC or SCC tumors may represent coincidental rather than causal infection, and that these tumors share other noninfectious risk factors.