Yes, although most cancer cells arise from within the body, certain types of cancer may actually be related to infectious diseases—mostly by viruses, but also bacteria and parasites may have an effect. Currently, it is estimated that infectious diseases may play a role in as much as 18 percent of human cancers worldwide. For example, infection by hepatitis B and hepatitis C can cause a chronic viral infection that leads to liver cancer— the most recent estimates are about 1 in 200 people for hepatitis B and 1 in 45 people for hepatitis C annually.