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Cancer: At a Glance

By The Manual's Editorial Staff,

A cancer is an abnormal growth of cells (usually derived from a single abnormal cell). Cancer cells have lost normal control mechanisms and thus are able to grow and multiply continuously, invade adjacent tissues, and spread to distant parts of the body. Cancerous (malignant) cells can develop from any tissue in the body.

For a full discussion, see Overview of Cancer.

Who Is at Risk of Cancer?

Many genetic and environmental factors can increase a person’s risk of cancer. But not all people who have risk factors develop cancer. So people should be alert for warning signs and follow the recommendations for cancer screening, such as those for colonoscopy, mammography, and skin cancer screening.

Cancer is much less common among children than among adults:

  • Each year, fewer than 11,000 children aged 0 to 14 years are diagnosed with cancer compared with 1.4 million adults.

What Are the Warning Signs of Cancer?

Some warning signs of cancer are general. That is, they are usually caused by something other than cancer and, when caused by cancer, do not help pinpoint any particular cancer. Still, their presence can help direct doctors to do the physical examinations and laboratory tests necessary to exclude or confirm a diagnosis.

Other warning signs are much more specific and steer doctors to a particular kind of cancer or location.

Some warning signs of possible cancer are

How Is Cancer Diagnosed?

In people with warning signs or symptoms of cancer, doctors do tests, including

  • Blood tests

  • Imaging

  • Biopsy

How Can You Reduce the Risk of Getting Cancer?

According to the American Cancer Society, the risk of developing certain cancers may be reduced by making lifestyle changes.

Measures known to reduce the risk of cancer:

  • Avoiding smoking or exposure to tobacco smoke

  • Avoiding occupational carcinogens (for example, asbestos)

  • Avoiding prolonged exposure to sunlight without sunscreen protection

  • Not using hormone therapy (for example, estrogen and progesterone) for symptoms of menopause

Measures that may reduce the risk of cancer:

  • Limiting intake of high-fat foods, particularly from animal sources (for example, high-fat meats and whole-fat dairy products)

  • Limiting intake of processed meat

  • Increasing intake of fruits and vegetables

  • Increasing intake of whole-grain foods

  • Being physically active

  • Keeping weight below the obese level

How specific foods and supplements affect the risk of getting cancer are unclear, but there is good evidence that obesity increases the risk of a number of cancers.

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