Infectious causes of cancer

Estimates place the worldwide risk of cancers from infectious causes at 16.1%. Viral infections are risk factors for cervical cancer, 80% of liver cancers, and 15–20% of the other cancers. This proportion varies in different regions of the world from a high of 32.7% in Sub-Saharan Africa to 3.3% in Australia and New Zealand.

A virus that can cause cancer is called an oncovirus or tumor virus. These include the human papillomavirus, which is associated with cervical carcinoma and nasopharyngeal carcinoma; Epstein-Barr virus, which is associated with a variety of Epstein-Barr virus-associated lymphoproliferative lymphomas; Kaposi's sarcoma herpesvirus, which is associated with Kaposi's sarcoma and primary effusion lymphoma; hepatitis B and hepatitis C viruses which are associated with hepatocellular carcinoma; human T-cell leukemia virus-1, which is associated with adult T-cell leukemia/lymphoma; and bovine leukemia virus, which is associated with breast cancer. Bacterial infection may also increase the risk of cancer, as seen in Helicobacter pylori-induced stomach cancer. Parasitic infections strongly associated with cancer include Schistosoma haematobium (squamous cell carcinoma of the bladder) and the liver flukes, Opisthorchis viverrini and Clonorchis sinensis (cholangiocarcinoma).