Many people are surprised to learn that cancer can be caused by an infection. Infections with certain viruses and bacteria have been recognized as risk factors for several types of cancer in humans.

Worldwide, infections are linked to about 15% to 20% of cancers. This percentage is even higher in developing countries, but it is lower in the developed countries. This is partly because certain infections are more common in developing countries, and partly because some other risk factors for cancer, such as obesity, are more common in developed countries.

Hepatitis Causing Liver Cancer

People who are infected with hepatitis B virus (HBV) or hepatitis C (HCV) virus may develop a chronic infection that can lead to cirrhosis. The damage that results increases the risk of liver cancer (hepatocellular carcinoma). The risk of liver cancer is greater for people who have chronic HBV or HCV infection than for the general population. These viruses are transmitted by unsafe sex or unsafe blood products. Presently HBV can be prevented by vaccination. There is no vaccine for HCV.

HPV Infection

Human papillomavirus (HPV) is the most common sexually transmitted infection with most sexually active men and women being exposed to the virus at some point during their lifetime. HPV can cause cervical and other cancers including cancer of the vulva, vagina, penis, or anus. It can also cause cancer in the back of the throat, including the base of the tongue and tonsils (called oropharyngeal cancer). This infection can be prevented by taking a vaccine which is presently indicated for young women to prevent cervical cancer.

Stomach Cancer

Helicobacter pylori (H pylori) bacteria which infects stomach causing gastritis can damage the inner layer of stomach. This damage can lead to cancer over years. H. pylori infection is common in developing countries and is spread by unhygienic food. There are tests to diagnose this and treatment to cure the infection. Prevention is by maintaining food hygiene and quality.

Spread of These Cancers

Many of the infections that influence cancer risk can be passed from person to person, but cancer itself cannot. A healthy person can’t “catch” cancer from someone who has it.

So to conclude, there is an unequal burden of infection-related cancers among the developing countries. This is particularly true for cervical cancer caused by certain genital papilloma viruses, liver cancer caused by the hepatitis B and C viruses, and stomach cancer caused by H. pylori.  

Even though the infections described here can raise a person’s risk of certain types of cancer, most people with these infections never develop cancer. The risk of developing cancer is also influenced by other factors. For example, infection with Helicobacter pylori (H pylori) bacteria might increase your risk of stomach cancer, but what you eat, whether or not you smoke, and other factors also affect your risk.