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  » Cancer: risk chart  »  Cancer Causes (Why do people get cancer?)

Why do people get cancer?

  • Do a lot of people have cancer?
  • What does a cancer cell look like?
  • Can cancer be prevented?
  • Who is at risk of getting cancer?


Ninety percent of cancers develop because of complex interactions between our bodies, our lifestyles, our genetic makeup and our environment. Scientists have discovered different factors that cause cancer. Research shows that tobacco is estimated to cause 30 percent of all cancer deaths, poor diet 35 percent, reproductive and sexual behavior seven percent, work-related causes four percent and the environment itself causes three percent.

Scientists believe that genetic changes, whether inherited or acquired, are the basic cause of cancer. Some scientific theories do suggest that cancer may be a hereditary disease because each individual's make-up may make them more susceptible to certain cancers. About 50 of the more than 120 different types of cancer occasionally run in families.

Most of the current scientific evidence indicates that a normal cell can become transformed into a cancer cell when certain genes become activated. Recent work in cancer biology concerns the study of oncogenes, a specific gene that participates in changing a normal cell into a cancer cell. It is thought that an oncogene might be present in an inactive form in normal cells and is some way activated to create cancer cells.

As mentioned, the nature of a person's work or the working environment can also be a factor in developing cancer. The chart below identifies several cancer-causing agents, occupations where this exposure occurs and the types of cancers that can develop.





Farmers, Sailors,
Lifeguards, Everyone



Underground Miners

(example- uranium)


Asbestos workers,
Insulation workers



Workers who use glue,
varnishes, etc.





Things to Talk About

  1. Can you develop cancer at any age?
  2. Are some cancers more deadly than others?
  3. What substances are carcinogens? What different types of cancer may they cause?


Carcinogen--A substance or agent that encourages the growth of cancer cells.
Carcinoma--A cancer which is a malignant growth of epithelial tissue or the tissue that forms the skin or blood vessels in an organism (e.g., the surface cells of the skin and the inside of the blood vessels).
Sarcoma--A cancer which is the malignant growth of connective tissue.
Leukemia--Cancer of the blood-forming tissues.


  • Goldfarb, Ronald H. Cancer Growth and Progression - Fundamental Aspects of Cancer. Norwell, MA: Kluwer Academic Publishers, 1989.
  • Lafond, Richard. Cancer: The Outlaw Cell. Washington, D.C.: American Chemical Society, 1988.
  • Oppenheimer, Steven B. "Advances in Cancer Biology." The American Biology Teacher, January, 1987, pp. 11-15.
  • Oppenheimer, Steven B. "Tumor Suppressor Genes: A Key to the Cancer Puzzle?" The American Biology Teacher, January, 1991. pp. 22-24.

Additional Sources of Information

  • American Cancer Society 1599 Clifton Road, N.E., Atlanta, GA 30329