In 2008, Merkel cell polyomavirus (MCV) was discovered as a causative agent of MCC, suggesting that integration of the viral genetic material to the cell is responsible for the virus induced pathogenesis, and the molecular mechanism associated with the disease pathogenesis has been reported in diverse literatures, which involves p53, PTEN, Ras/MAPK, and PI3K/Akt. The gene discussed is PIK3CA; the disease is Merkel cell skin cancer.