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Cancer Screening Overview (PDQ®)

  • Last Modified: 07/02/2014

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What Is Cancer Screening?



Cancer screening is looking for cancer before a person has any symptoms.

Screening tests can help find cancer at an early stage, before symptoms appear. When abnormal tissue or cancer is found early, it may be easier to treat or cure. By the time symptoms appear, the cancer may have grown and spread. This can make the cancer harder to treat or cure.

It is important to remember that when your doctor suggests a screening test, it does not always mean he or she thinks you have cancer. Screening tests are done when you have no cancer symptoms.

There are different kinds of screening tests.

Screening tests include the following:

  • Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
  • Laboratory tests: Medical procedures that test samples of tissue, blood, urine, or other substances in the body.
  • Imaging procedures: Procedures that make pictures of areas inside the body.
  • Genetic tests: Tests that look for certain gene mutations (changes) that are linked to some types of cancer.

Screening tests have risks.

Not all screening tests are helpful and most have risks. It is important to know the risks of the test and whether it has been proven to decrease the chance of dying from cancer.

Some screening tests can cause serious problems.

Some screening procedures can cause bleeding or other problems. For example, colon cancer screening with sigmoidoscopy or colonoscopy can cause tears in the lining of the colon.

False-positive test results are possible.

Screening test results may appear to be abnormal even though there is no cancer. A false-positive test result (one that shows there is cancer when there really isn't) can cause anxiety and is usually followed by more tests and procedures, which also have risks.

False-negative test results are possible.

Screening test results may appear to be normal even though there is cancer. A person who receives a false-negative test result (one that shows there is no cancer when there really is) may delay seeking medical care even if there are symptoms.

Finding the cancer may not improve the person's health or help the person live longer.

Some cancers never cause symptoms or become life-threatening, but if found by a screening test, the cancer may be treated. There is no way to know if treating the cancer would help the person live longer than if no treatment were given. In both teenagers and adults, there is an increased risk of suicide in the first year after being diagnosed with cancer. Also, treatments for cancer have side effects.

For some cancers, finding and treating the cancer early does not improve the chance of a cure or help the person live longer.

The PDQ cancer screening summaries are written to help people learn about screening tests.

Scientists study screening tests to find those with the fewest risks and most benefits. The PDQ cancer screening summaries are based on the results of these studies and other scientific information about cancer risk and screening tests. The summaries are written to give readers the most current information about standard screening tests and tests that are being studied in clinical trials.

It can be hard to make decisions about screening tests. Before having any screening test, you may want to discuss the test with your doctor.