Biological factors include viruses, bacteria and parasites. It is now believed that 15% of all cancers in humans are caused by biologic factors. The main culprits are DNA viruses, including papillomavirus, which causes cervical cancer, hepatitis B virus, which causes liver cancer, and EBV, which causes lymphoma and nasopharyngeal cancer. RNA viruses that can cause tumors include human T-cell leukemia virus type I (abbreviated as HLTV-Ⅰ), which causes T-cell leukemia lymphoma; human immunodeficiency virus, which causes Kapuzi’s sarcoma and lymphoma; and hepatitis C virus, which causes hepatocellular carcinoma. Prize. The best example of a bacterium that can also cause cancer is a bacterium called Helicobacter pylori (abbreviated as Hp), which has also been definitely linked to gastritis and stomach cancer. It is also well established that Schistosoma haematobium, a parasitic worm, can cause cancer of the colon and liver, and that Schistosoma waxeri can cause cancer of the bile ducts.