MCPyVpositive

MCPyV-positive refers to tumors that harbor and express Merkel cell polyomavirus (MCPyV), most often in the context of Merkel cell carcinoma (MCC). Tumors are classified as MCPyV-positive or MCPyV-negative based on the presence of MCPyV DNA and the expression of viral proteins within tumor cells. This status is used as a biomarker to aid in diagnosis and, to some extent, prognosis and treatment planning.

Detection and validation rely on multiple assays. Immunohistochemistry can detect viral antigens, notably the MCPyV large T antigen, using antibodies such as CM2B4. Molecular methods, including PCR or sequencing, identify MCPyV DNA and assess viral integration into the host genome. The combination of viral DNA presence and clonal integration supports a virus-driven mechanism of oncogenesis in MCC.

Biology and clinical features differ between MCPyV-positive and MCPyV-negative MCC. In MCPyV-positive tumors, viral genome integration with expression of truncated large T antigen and small T antigen drives oncogenesis with relatively fewer host mutations, often resulting in a lower overall mutation burden compared with virus-negative tumors, which are more commonly associated with UV-related mutational signatures. These differences can influence histology, immune infiltrates, and potentially prognosis.

Prognosis and treatment considerations vary in the literature, but MCPyV status is primarily used as a diagnostic and prognostic biomarker. MCPyV-positive MCC generally has distinct molecular characteristics and may respond to therapies that leverage viral antigens or the patient’s immune response. Standard MCC management—surgical excision, radiotherapy for localized disease, and immune checkpoint inhibitors for advanced cases—applies regardless of viral status, with ongoing research exploring virally targeted strategies.