More than just oncogenes: mechanisms of tumorigenesis by human viruses

Most humans are infected with at least one of the known human cancer viruses during their lifetimes. While the initial infection with these viruses does not cause major disease, infected cells can acquire cancer hallmarks, particularly upon immunosuppression or exposure to co-carcinogenic stimuli. Even though cancer formation represents a rare outcome of a viral infection, approximately one out of eight human cancers has a viral etiology. Viral cancers present unique opportunities for prophylaxis, diagnosis, and therapy, as demonstrated by the success of HBV and HPV vaccines and HCV antivirals in decreasing the incidence of tumors that are caused by these viruses. Here we review common characteristics and mechanisms of action of the human oncogenic viruses.