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Last updated: 6-Jul-2011

Infections

The fact that viral infections can cause cancer has been suspected for over a 100 years, beginning with the observed connection between cervical cancer and multiple sexual partners.[1] By 1911, the Journal of the American Medical Association had reported on the association between viruses and cancer in animals. Proof of causality has proven more elusive, but slowly the research support for implicating specific pathogens has emerged.[2] The International Agency for Research on Cancer has now confirmed 7 viral or bacterial agents as carcinogenic in humans.[3] Cancers of the stomach, liver and cervix rank among the most prevalent ones with a viral or bacterial origin.

Several parasitical worms or flukes (known collectively as helminths) have been added to the list of proven or probable carcinogens. In fact, the blood fluke called Schistosoma haematobium was linked with bladder carcinoma as early as the middle of the 19th century.

The etiology and mechanisms of infection-based cancer have been important areas of study, generating several Nobel prizes in recent years.[4] Two features have spurred on the research:

  • the study of viral carcinogenesis has offered a wealth of insight into the general cellular mechanisms of cancer.[5]
  • an infectious origin for a particular cancer holds out the promise that such disease is actually preventable.
The impact of infection-associated cancer is more substantial than sometimes realized by the general public. Kuper and colleagues noted that “following tobacco use, infections as a group may be the most important preventable cause of cancer in humans.”[6] Worldwide, the proportion of cancer attributable to infections with viruses, bacteria and parasites is estimated to be 15-16%, or 1.2 to 1.5 million new cases a year.[7],[8],[9] Some of these agents are less common in developed countries, so the proportion of cancers associated with infections may be half as much as the global rate.[10] For instance, in the US, about 7% of total cancer incidence has been attributed to one or more infectious agent.[11] It is important to note that improved serological techniques may eventually reveal an even greater role for infection in the phenomenon of carcinogenesis.[12]

We will provide an overview of the pathogens associated with cancer, their disease mechanism and burden, before turning to a detailed presentation on each agent. The latter material will especially focus on the prevention and other management strategies that could be used to reduce the prevalence of infection-related cancer.

[1] Moscicki AB, Palefsky J, Gonzales J et al. Human papillomavirus infection in sexually active adolescent females: prevalence and risk factors. Pediatric Research. 1990; 28(5): 507-13.

[2] Such agents are referred to as being carcinogenic or oncogenic.

[3] Herrera LA, Benitez-Bribiesca L, Mohar A et al. Role of infectious diseases in human carcinogenesis. Environmental & Molecular Mutagenesis. 2005; 45(2-3): 284-303. See Appendix A.

[4] Kuper H, Adami HO, Trichopoulos D. Infections as a major preventable cause of human cancer. Journal of Internal Medicine. 2000; 248(3): 171-83.

[5] Butel JS. Viral carcinogenesis: revelation of molecular mechanisms and etiology of human disease. Carcinogenesis. 2000; 21(3): 405-26.

[6] Kuper H, Adami HO, Trichopoulos D. Infections as a major preventable cause of human cancer. Journal of Internal Medicine. 2000; 248(3): 171-83.

[7] Evidence-based Cancer Prevention Strategies for NGOs. International Union Against Cancer; 2004.

[8] Kuper H, Adami HO, Trichopoulos D. Infections as a major preventable cause of human cancer. Journal of Internal Medicine. 2000; 248(3): 171-83.

[9] Pisani P, Parkin DM, Munoz N et al. Cancer and infection: estimates of the attributable fraction in 1990. Cancer Epidemiology, Biomarkers & Prevention. 1997; 6(6): 387-400.

[10] Herrera LA, Benitez-Bribiesca L, Mohar A et al. Role of infectious diseases in human carcinogenesis. Environmental & Molecular Mutagenesis. 2005; 45(2-3): 284-303.

[11] Mueller NE. Cancers caused by infections: unequal burdens. Cancer Epidemiology, Biomarkers & Prevention. 2003; 12(3): 237s.

[12] Kuper H, Adami HO, Trichopoulos D. Infections as a major preventable cause of human cancer. Journal of Internal Medicine. 2000; 248(3): 171-83.