[Viruses: an important cause of human cancer]

More than 90 years have passed since Peyton Rous reported that a tumor was transmitted between chickens like an infection disease. Currently the viruses are considered the second most important cause of cancer in humans and contribute to 10 to 20% of all cancer cases in the world, some of them being very common, like cervical and hepatocellular carcinomas. Human recognized cancer viruses include HPV, HBV, HCV, EBV, HHV-8 and HTLV-1. The knowledge of how viruses participate in the ethiopathogeny of cancer will allow fighting the disease with similar strategies than those that we use to control those infective agents now days. Great efforts are being initiated to decrease incidence of the neoplasms by preventing the initial infection or by prophylactic vaccination.