Most (but not all) Merkel cell carcinomas are positive for the Merkel cell polyomavirus.
The relationship between the tumor and the virus is uncertain. One hypothesis is that the virus is oncogenic, especially in immunocompromised patients. A second is that the virus has become incorporated into tumor cells as a passenger.
The fact that not all Merkel cell carcinomas are positive for the virus has raised questions about the oncogenicity of the virus. However, there could be different types of Merkel cell carcinoma, some triggered by the virus and others not.
Significance of identifying the virus:
(1) it can help to support the diagnosis in a questionable case
(2) it can be a target for treatment (antiviral agent, engineered T cells, vaccine, other)
(3) viral load maycorrelate with tumor activity and survival (worse with high viral load)
(4) the titer of antibodies against the virus may correlate with prognosis (worse with low titers)
