Human polyomaviruses 6 and 7 are not detectable in Merkel cell polyomavirus-negative Merkel cell carcinoma

BACKGROUND: Merkel cell carcinoma (MCC) has a high degree of association with Merkel cell polyomavirus (MCPyV). However, no reliable microscopic, clinical, phenotypic or molecular differences have been identified that distinguish MCPyV-positive from MCPyV-negative MCC, raising the possibility that a related polyomavirus may be present in MCPyV-negative cases. Recently, two additional human polyomaviruses, human polyomaviruses 6 and 7 (HPyV6 and HPyV7), were shown to be present in normal skin of healthy subjects along with MCPyV. Consequently, we sought to determine if the presence of HPyV6 of HPyV7 could account for MCPyV-negative MCC. METHODS: DNA was extracted from formalin-fixed, paraffin-embedded tissue blocks of 28 previously characterized MCC cases that included 22 MCPyV-positive and 6 MCPyV-negative samples. Real-time polymerase chain reaction targeting three viral regions was used to detect HPyV6 and HPyV7. RESULTS: None of the 28 MCC cases, which included both MCPyV-positive and negative cases, showed amplifiable HPyV6 or HPyV7 DNA. CONCLUSIONS: While MCPyV, HPyV6, and HPyV7 are part of normal skin flora and show a high degree of sequence similarity, there is no evidence of an association between HPyV6 and HPyV7 and MCC in this case series. This result argues against a role for HPyV6 and HPyV7 in the pathogenesis of MCPyV-negative MCC.