Cancer causing infections
While cancer is not infectious there are a number of infections that either directly cause cancer, or increase the risk of cancer.
In fact almost 22% of cancer deaths in the developing world and 6% in industrialized countries are caused by chronic infections. For example hepatitis B or C virus are know to cause cancer of the liver, human papillomavirus is linked to cervical cancer and helicobacter pylori bacteria increases the risk of stomach cancer.
Interventions such as immunization, treatment of infections and behaviour change can reduce exposure to specific risk factors.