In 67-100% of cutaneous Merkel cell
carcinomas (MCC) the Merkel cell polyomavirus (MCPyV) integrates into the host genome. Mutations and deletions truncating the C-terminal helicase domain of the
T-antigen (TAg)
protein have been detected in these MCCs, but not in healthy skin specimens. C-terminal deletions of the TAg
nucleic acid sequences are characteristic for about 38% of these cases. While the association of MCPyV with MCC has been proven, it is unknown whether MCPyV may play a similar role in other
tumor entities. We describe in detail the development and validation of a novel Merkel cell polyomavirus TAg C-terminus deletion assay (MCPyV ΔC-TAg). The triplex real-time PCR quantifies the N- and C-terminal part of the MCPyV TAg gene and the cellular β-
globin gene. By comparing the copy numbers of the N- and C-terminal part, deletions of the MCPyV TAg C-terminus are rapidly identified. MCPyV ΔC-TAg was used to assess the physical state of MCPyV TAg in a large series of 55 MCCs, 15 cutaneous
lymphomas and 47 forehead smears of healthy individuals. Neither
DNA positivity nor viral load was able to discriminate MCCs from the other different types of samples. However, deleted TAg C-terminus sequences were detected only in MCPyV positive MCCs (39%). Consequently, detection of deleted C-terminal TAg sequences appears to be a highly specific
surrogate marker for virally induced
malignancy and should be used to support novel assumed MCPyV-
tumor associations. The study further supports the notion that MCPyV does not play a role in cutaneous
lymphoma pathogenesis.