• Causes of Cancer

    Carcinogens are factors or exposures in a person’s environment that contribute to the development of cancer-promoting genetic mutations. There are many known carcinogens, the most common of which can be categorized into the following groups:

    Dietary Factors

    Diet is considered a possible risk factor in a number of types of cancer, particularly colon, breast, endometrial, and gall bladder cancers. A lack of roughage and bulk in the average American diet and high levels of dietary fats, particularly unsaturated fats are thought to be two of the key dietary cancer-causing agents. According to research, limiting fat consumption and calorie intake appears to be one way to decrease cancer risk.

    Alcohol

    Drinking large amounts of alcohol is another risk factor for several types of cancer, including liver, breast, gastric, and those of the mouth, throat, and esophagus. This risk is heightened even further when combined with tobacco use. For example, in heavy smokers or heavy drinkers, the risk of developing cancer of the esophagus is approximately six times greater than for nonsmokers/nondrinkers. Similarly, oropharyngeal cancer (cancer of the mouth, tongue, and oral cavity) is rare in people who neither smoke nor drink. Smoking or drinking alone will greatly increase the risk of cancer, and both together represent an even higher risk of developing cancer in any of the target organs.

    Smoking

    Cigarette smoke contains a variety of chemicals that can cause cancer, both in the respiratory tract and oral cavity, and in other sites such as the kidney, bladder and gastrointestinal tract. Avoiding smoke, either from smoking or secondhand smoke, is one of the best ways to reduce one’s personal cancer risk.

    Viruses

    Viruses are small infectious agents that cannot reproduce on their own. Instead, they enter into living cells and cause them to produce more copies of the virus. Like cells, viruses carry genes, which they may insert into the chromosomes of the infected cell. This manipulation of the infected cell’s genetic makeup by the virus can substantially increase its risk of becoming cancerous.
    Out of the many viruses we come in contact with every day, only a few have been linked to cancer. Although cancers cannot be spread from person to person, the viruses that cause them can. Women with multiple sexual partners or whose partners have had multiple sexual partners, for example, are at increased risk for cervical cancer. This is because human papillomavirus (HPV) , a common sexually transmitted infection, may cause this disease. Table 1 lists some common viruses and their associated cancers. In addition, infection with HIV is associated with an increase in a variety of cancers, in part because HIV reduces the body’s natural immune defenses against cancer.
    Table 1: Common Viruses and the Cancers With Which They are Associated
    Virus Type of Cancer
    Epstein-Barr virus Burkitt’s lymphoma
    Human papillomavirus Cervical cancer
    Hepatitis B virus Liver cancer
    Human T-cell lymphotrophic virus Adult T-cell leukemia
    Kaposi’s sarcoma-associated herpesvirus Kaposi’s sarcoma

    Chemical Toxins

    Repeated contact with certain chemical toxins through lifestyle, workplace, and medical exposures may lead to cancer by directly damaging the DNA in genes. Tobacco, which contains hundreds of cancer-promoting toxins, is the best known chemical carcinogen. While chewing tobacco may lead to cancer of the mouth, smoking tobacco is associated with cancer in many parts of the body. Workplace exposures are a common source for chemical carcinogens. Cancer rates in construction workers, who handle asbestos, for example, are about 10 times higher than in unexposed workers. Table 2 lists some common carcinogenic chemicals you may be exposed to in your workplace.
    Table 2: Common Carcinogens in the Workplace
    Carcinogen Occupation Type of Cancer
    Arsenic Mining, pesticide workers Lung, skin, liver
    Asbestos Construction workers Lung, mesothelioma
    Benzene Petroleum, rubber, chemical workers Leukemia
    Chromium Metal workers, electroplaters Lung
    Leather dust Show manufacturing Nasal, bladder
    Naphthylamine Chemical, dye, rubber workers Bladder
    Radon Underground mining (also in some homes) Lung
    Soots, tars, oils Coal, gas, petroleum workers Lung, skin, liver
    Vinyl chloride Rubber workers, polyvinyl chloride Liver
    Wood dust Furniture manufacturing Nasal

    Although doctors take care to protect their patients from harmful substances, certain medications and therapeutic procedures are known to raise the risk of cancer. Hormone replacement therapy, for example, has recently been shown to slightly increase the risk of breast cancer in post-menopausal women.

    Radiation

    Ultraviolet radiation from the sun is a common cause of skin cancer. In fact, basal and squamous cell carcinoma of the skin are the most common cancers and among the most easily treated and cured. Malignant melanoma, a cancer of the pigmented cells, is a far less common, but much more serious form of skin cancer.
    Ground sources of ionizing radiation may also cause cancer. For example, survivors of the atomic bomb dropped on Hiroshima and Nagasaki in 1945 have a higher-than-expected incidence of leukemia and several other cancers, as do people exposed to radiation from nuclear reactor leaks. The risk of developing cancer and the type of cancer depends on the dose of radiation as well as the length of exposure. Repeated low-dose exposure over a long period produces different cancers than those encountered after a single high dose such as that found among survivors of Hishima and Nagasaki. Similarly, people exposed to excessive and prolonged radiation from x-rays also have an increased risk of cancer. And, uranium mine workers get lung cancer more commonly than the general population.

    References

    Detailed guide. American Cancer Society website. Available at: http://www.cancer.org/ . Accessed August 1, 2008.

    Bast RC, Kufe DW, Pollock RE, et al. Eds. Cancer Medicine . 5th ed. Hamilton, ON: Decker Inc; 2000.

    Cancer. Merck Manual of Medical Information website. Available at: http://www.merck.com/mrkshared/mmanual%5Fhome/contents.jsp . Accessed March 25, 2003.

    American Cancer Society. Cancer Facts & Figures 2003 . Atlanta, GA: American Cancer Society, Inc;2003.

    Finley RS, Balmer C. Concepts in Oncology Therapeutics . 2nd ed. Bethesda, MD: American Society of Health-System Pharmacists;1998.

    Fox SI. Human Physiology . 4th ed. Dubuque, IA: William C. Brown Publishers; 1993.

    Defining cancer. National Cancer Institute website. Available at: http://www.cancer.gov/cancertopics/what-is-cancer . Accessed August 1, 2008.

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