What is the pathogenesis of MCC?

MCC is extremely rare before age 50 years, and the incidence increases steeply after 65 years of age, suggesting an accumulation of oncogenic events. Immunosuppression is likely involved in the pathogenesis, as MCC incidence is increased approximately 11-fold for persons with AIDS and 5-fold for persons who have undergone organ transplantation. The majority of tumors present on sun-exposed areas, and the risk of MCC may be particularly high with prior psoralen and ultraviolet A treatment (PUVA) suggesting that UV radiation contributes to the etiology of this malignancy. More recently, the viral genome of polyomavirus (Merkel cell polyomavirus) was detected in MCC, and there is accumulating evidence to suggest a direct mechanistic role for the virus in the pathogenesis of MCC.

Feng H, Shuda M, Chang Y, Moore PS: Clonal integration of a polyomavirus in human Merkel cell carcinoma, Science 319:1096–1100, 2008.