Viral and chemical carcinogens

In 1915, Katsusaburo Yamagiwa and Koichi Ichikawa at Tokyo University, induced cancer in lab animals for the first time by applying coal tar to rabbit skin. More than 150 years had passed since clinician John Hill of London recognized tobacco as a carcinogen (a substance known or believed to cause cancer in humans). Many more years passed before tobacco was “rediscovered” as the most destructive source of chemical carcinogens known to man.

Today we recognize and avoid many specific substances that cause cancer: coal tars and their derivatives (like benzene), some hydrocarbons, aniline (a substance used to make dyes), asbestos, and many others. Radiation from a variety of sources, including the sun, is also known to cause cancer. To ensure the public’s safety, the government has set safety standards for many substances, including benzene, asbestos, hydrocarbons in the air, arsenic in drinking water, and radiation.

In 1911, Peyton Rous, at the Rockefeller Institute in New York, described a type of cancer (sarcoma) in chickens caused by what later became known as the Rous sarcoma virus. He was awarded the Nobel Prize for that work in 1968. Several viruses are now linked to cancer in humans, too:

• Long-standing infection with the hepatitis B or C viruses can lead to cancer of the liver.
• One of the herpes viruses, the Epstein-Barr virus, causes infectious mononucleosis and has been linked to non-Hodgkin lymphomas and nasopharyngeal cancer.
• The human immunodeficiency virus (HIV) is associated with an increased risk of developing several cancers, especially Kaposi sarcoma and non-Hodgkin lymphoma.
• Human papilloma viruses (HPVs) have been linked to many cancers, especially those of the cervix, vulva, vagina, anus, and penis. Some head and neck cancers (mostly the tongue and tonsils) are linked to the high-risk types of HPV, too.

As of 2011, the World Health Organization’s International Agency for Research on Cancer (IARC) has identified more than 100 chemical, physical, and biological carcinogens. Many of these associations were recognized long before scientists understood much about how cancer develops. Today, research is discovering new carcinogens, explaining how they cause cancer, and providing insight into ways to prevent cancer.