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Understanding Screening Trials
    Updated: 03/15/2002
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Screening and Testing to Detect Cancer

What Is a Clinical Trial?

Along with cancer treatment clinical trials (which test whether a new drug or procedure is effective) and prevention trials (which test drugs or other agents to find out if they reduce the risk for cancer), there is a third type of study: screening trials.

Screening trials test new ways of finding cancer in people before they have any cancer symptoms. These methods of detecting cancer, often called screening tests, can include:

  • Imaging tests - tests that produce pictures of areas inside the body.
  • Laboratory tests - tests that check blood, urine, and other body fluids and tissues.
  • Genetic tests - tests that look for inherited genetic markers linked to some types of cancer.

An important note: the same tool or technique can be used either for screening or for diagnosis, depending on the situation in which it is used.

Screening involves checking for cancer (or for conditions that may lead to cancer) in a person who does not have any symptoms of the disease. Diagnosis is looking for cancer in a patient who usually has signs and/or symptoms of the disease.

For example, mammography (x-ray study of the breast) can be used to screen for cancer or to diagnose cancer. When a healthy woman gets a routine mammogram as part of a yearly checkup, the mammogram is a screening tool; it is being used to check for cancer even though there are no signs or symptoms of the disease.

However, when a woman gets a mammogram because of unusual breast changes she or her doctor has noticed (such as pain in the breast, or a lump in the breast), the mammogram is being used as a diagnostic tool. The diagnostic mammogram will help the doctor determine what additional tests (such as a biopsy) are needed.

The goal of screening trials is to develop screening tools that will catch cancer earlier. For many types of cancer, detecting and treating the disease at an early stage can result in an improved outcome -- a better chance to shrink the cancer, minimize its effects, or cause it to go away completely.

Cancer tests now considered standard that were once experimental include X-ray mammography for breast cancer and Pap tests for cervical cancer.

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