Questions About Cancer? 1-800-4-CANCER

Understanding Cancer Series

  • Posted: 01/28/2005
  • Reviewed: 09/30/2009

Slide 24

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What Causes Cancer?

Cancer is often perceived as a disease that strikes for no apparent reason. While scientists don't yet know all the reasons, many of the causes of cancer have already been identified. Besides intrinsic factors such as heredity, diet, and hormones, scientific studies point to key extrinsic factors that contribute to the cancer's development: chemicals (e.g., smoking), radiation, and viruses or bacteria.

What Causes Cancer?