Viruses and Bacteria Cause One in Six New Cancer Cases
Infections with bacteria, viruses, and parasites have been linked to certain cancers – such as the human papillomavirus (HPV) with cervical cancer - but the problem may be more widespread than that. A new study suggests that one in six new cancer cases may be due to infections that are largely preventable or treatable.
Dr. Catherine de Martel and Dr. Martyn Plummer of the International Agency for Research on Cancer (IARC) examined data on global cancer incidence for 2008 using the IARC classification of carcinogenic infectious agents. Of the 12.7 million total new cancer cases that year, 2 million (16.1%) were attributable to infections. Most of these cancer-causing infections were of the gut, liver, cervix, and uterus.
The top four agents responsible for the vast majority of infection-related cancers were Helicobacter pylori, Hepatitis B and C, and Human Papillomavirus. Between them, these three viruses and one bacterium were responsible for 1.9 million cases.
Helicobacter pylori, or H. pylori, is a common bacteria, particularly in developing countries. It is found in the stomach of about two-thirds of the world’s population and causes more than half of peptic ulcers worldwide by damaging the mucous coating that protects the stomach and duodenum (upper small intenstine). It is a major cause of gastric (stomach) cancer and is associated with an increased risk of gastric mucosa-associated lymphoid tissue (MALT) lymphoma. Researchers think that H. pylori is transmitted through contaminated food or water or through direct mouth-to-mouth contact, notes the National Digestive Diseases Information Clearinghouse (NDDIC).
Viral hepatitis is a disease affecting the liver. There are three types – A, B and C, with the latter two most closely associated with damage that can result in liver cancer (hepatocellular carcinoma). Hepatitis B (HBV) and Hepatitis C (HCV) are contracted through contact with the blood and body fluids of an infected person. You may get HBV if you have sex, share needles, or share personal items such as a razor with an infected person. Tattoo and piercing instruments that are not cleaned well and still contain contaminated blood can also transmit the virus.
Human Papillomavirus (HPV) is the most common sexually transmitted infection (STI). There are more than 40 HPV types that can infect the genital areas of males and females. In 90% of cases, the body’s immune system clears HPV naturally within two years. But sometimes, infection can lead to cancers such as cervical cancer, cancer of the vulva, vagina, penis, anus, and oropharynx (back of throat).
The proportion of infection-related cancer cases is about three times higher in less developed countries (22.9%) than more developed countries (7.4%). For example, only 3.3% of new cancer cases were due to infection in Australia and New Zealand, compared to 32.7% in sub-Saharan Africa.
The authors conclude that, "Application of existing public health methods for infection prevention, such as vaccination, safer injection practice, or antimicrobial treatments, could have a substantial effect on the future burden of cancer worldwide." Vaccines are available to protect against hepatitis B and human papillomavirus (HPV); Antibiotic treatment can clear the gut of H. pylori bacteria.
Catherine de Martel MD,Jacques Ferlay ME,Silvia Franceschi MD,Jérôme Vignat MSc,Freddie Bray PhD,David Forman PhD,Dr Martyn Plummer PhD. Global burden of cancers attributable to infections in 2008: a review and synthetic analysis. The Lancet Oncology - 9 May 2012