Merkel Cell Polyomavirus - Prevention, Diagnosis, and Treatment

Prevention, Diagnosis, and Treatment

Persons who have Merkel cell carcinoma with this virus are not infectious to others and no infectious restrictions are warranted. The reasons for this are: 1) the virus in tumors is already mutated and no longer can be transmitted from tumors, and 2) most persons are already naturally exposed to this virus as children and young adults by other asymptomatic carriers.

Based on current data, prevention advice for MCC is similar to other skin cancers, such as avoiding sun burns and unnecessary sun exposure together with use of sun lotion. This may prevent mutations in the virus that increase risk for MCC among those already infected with MCV. Persons with immunosuppression (e.g., AIDS or transplant patients) are at higher risk for this cancer and may benefit from periodic skin examinations. Emergence of a painless lump that expands rapidly, especially among persons over age 50 or persons with immunosuppression, warrants examination by a physician. Biopsy of a Merkel cell tumor should readily provide a diagnosis and when caught early, has a good prognosis through standard treatment. At this time there are no vaccines or medications that can prevent MCV infection or prevent emergence of Merkel cell carcinoma.

Detection of the virus is still at a research phase and is generally not available as a clinical test. Detection of viral DNA is performed by PCR or by Southern blot. Caution is needed in interpreting results from PCR since it is prone to false-positive contamination and a substantial fraction of healthy skin samples may harbor low-level infection. Sequencing of the viral genome may determine whether or not tumor-specific mutations are present.

Antibodies have been developed to stain for T antigen in tumor tissues and appear to be specific for MCV-infected tumor cells. Blood tests have also been developed that show the majority of adults have been previously exposed to MCV and may continue to carry it as an asymptomatic infection.

Treatment guidelines do not differ for Merkel cell carcinoma infected with MCV or without MCV. A recent country-wide study from Finland suggests that MCV-positive tumors have a better prognosis than uninfected tumors (although this has not been found in other studies). If this is confirmed, routine detection of the virus may provide a future benefit for medical guidance. The virus itself is not known to be susceptible to current antiviral medications.

Recent studies reveal that the survivin oncoprotein is activated by MCV large T protein targeting the cellular retinoblastoma protein and that survivin inhibitors can delay tumor progression in animal models. Clinical trials are now being organized to determine whether this has any benefit in humans. The importance of this finding is that a promising rational drug target was uncovered within four years of the initial discovery of the virus and that other new treatments might be rapidly developed now that the cause of the cancer is known. MCV is a target for cell-mediated immune responses, and so important research efforts are being focused on immunologic therapies that may benefit MCC patients.