Some of this is used by the body and some goes to waste. Food is used to build the body, keep it in working order, and provide energy. Unfortunately, when chemically altering or arresting the course of one disease, these drugs can contribute to the development of other disease, including cancer. Some rare cancers are inherited, and usually appear at an early age. A number of rare hereditary disorders may predispose a person to cancer but the added action of one or more environmental factors is often needed for the cancer to develop.
Cigarette smoking increases the risk of cancer of the lung more than any other site.
Cigarette smoking also increases the risk of cancers of the larynx amd oesophagus. Although some viruses are associated with human cancers, other factors are believed to be responsible for the development of cancer. Viruses may make cells more susceptible to the effects of radiation or chemical carcinogens, for example. The advances in understanding cancer have been of little direct benefit to the cancer patient. For many cancers, the success of treatment is primarily determined by early detection, allowing the curative treatment of localized disease by surgery or radiotherapy.