Yes, viruses can cause cancer. In reading chapter 27, viruses contribute to about 15% of all human cancer cases and are capable of altering the human cells they infect. The virus triggers the expression of cancer-causing genes called oncogenes, which causes change in normal function; for example, the light switch always being on. However, virus-induced cancer is extremely difficult to occur because it requires a series of specific events. An examples of virus-induced cancer is the hepatitis B infection and the development of liver cancer.
