An
oncovirus is a
virus that can cause
cancer. This term originated from studies of acutely transforming
retroviruses in the 1950–60s, often called oncornaviruses to denote their RNA virus origin. It now refers to any virus with a DNA or RNA genome causing cancer and is synonymous with "tumor virus" or "cancer virus." The vast majority of human and animal viruses do not cause cancer, probably because of longstanding co-evolution between the virus and its host.