Though the link between HPV (human papillomavirus) infection and cancer has gained some notoriety recently, infections still go largely under appreciated as cancer risk factors.  But, they are large contributors to rates of cancer both globally, and in the United States.  Four percent of cancers in North American are linked to infections. This number increases to around 23 percent of cancers in lower income countries worldwide.

Certain infections can either directly or indirectly cause changes that can lead to cancer. This can happen because of the chronic inflammation that some infections cause or by an infectious agent (like a virus) changing the behavior of infected cells. Infections that compromise the immune system (like HIV) also increase cancer risk by making the body less able to defend against infections that can cause cancer.

Not surprisingly, infection-associated cancers are not a health burden borne equally by all. The poor living conditions and inadequate health care experienced by many people worldwide increase the likelihood of cancer resulting from chronic infections.

There are at least ten infectious agents that are known to increase the risk of cancer (see table), and several of them are quite common. Yet, in most instances, only a small proportion of those infected actually go on to develop cancer because it takes a unique set of factors along with the infection to turn normal cells cancerous.

Still, these infectious agents have a substantial impact on cancer globally. Of particular importance are HPV, hepatitis B and C viruses, and Helicobacter pylori. HPV is a sexually transmitted virus that is linked to numerous cancers, with cervical cancer being the most important. It’s estimated that almost all cervical cancers are caused by HPV infection. Hepatitis B and C infect the liver and together account for the large majority of liver cancer. Finally, Helicobacter pylori, a bacteria that infects the stomach, has been estimated to cause upwards of 75 percent of all stomach cancers, one of the most common cancers worldwide.

Infectious agents linked with cancer

Agent Type of cancer
Human papillomavirus (HPV) Cervix, vulva, anus, penis, head and neck
Hepatitis B virus (HBV) Liver
Hepatitis C virus (HCV) Liver
Helicobacter pylori Stomach
Epstein-Barr virus (EBV) Nasopharynx, Hodgkin’s disease, non-Hodgkin’s lymphoma
Human herpes virus type (HHV-8) Kaposi’s sarcoma
Human immunodeficiency virus Kaposi’s sarcoma, lymphoma
Human T-cell lymphotrophic virus type I (HTLV-I) Leukemia/lymphoma
Schistosomes Bladder
Liver flukes Bile duct

The promise of prevention is a bright spot when looking at the reach of infection-associated cancers. HPV vaccination of both girls and boys can prevent cervical cancer as well as penile, anal, and throat cancers.  The hepatitis B vaccine – which is growing in use – can prevent liver cancer.  Treatment of Helicobactor pylori likely reduces stomach cancer risk.  And improved screening for and treatment of Hepatitis C may lower liver cancer risk.  The U.S Preventive Services Task Force now recommends a one-time blood test for hepatitis C for adults born between 1945 and 1965.

Outside of vaccination and treatment, individuals can also lower the risk of infection-linked cancers by taking steps like avoiding blood exposure (by not sharing needles, for example), practicing safer sex and, for women, getting regular Pap tests and possibly HPV tests.

Further advances in vaccines – and in programs that administer them – offer much hope for prevention.