Understanding Cancer Screening Tests
Most cancers are easier to treat when they are found in their earlier stages. Doctors find cancers when they are small and normally undetectable by using screening tests such as mammography, blood tests, CT scans, and other tests. Often, doctors recommend screening tests when a person shows no sign of cancer because the tests can detect cancer before symptoms develop.
Many people, however, may not realize that there are controversies surrounding screening tests. Researchers have long been debating the value of mammograms, spiral CT (computerized tomography) scans for smokers, and the PSA (prostate-specific antigen) blood test. How do doctors decide what tests should be used for screening cancer? Who should get them? How often should they be done? How many people have to be tested before one life is saved? Why aren't there screening tests for all cancers?
Risks versus benefits
As with any tests, there are risks and benefits to screening tests. Benefits include finding precancerous cells before they develop into cancer (a result of regular Pap smears and colonoscopies) and finding cancer in its earlier stages when the tumor is small and contained and therefore easier to treat (a result of having a mammogram). Both of these can be done before the person even develops symptoms.
However, there are also risks, such as unnecessary and costly biopsies and treatments and wrong diagnoses. A false positive test suggests the person has cancer when they do not. A false negative test suggests the person does not have cancer when they do have it. Doctors should carefully weigh the benefits versus the risks of a screening test before suggesting that a patient have it.
Who decides what screening tests should be used?
Various professional groups and organizations such as the American Cancer Society, the National Cancer Institute, American Gastroenterological Association, and others review the research studies about screening tests and make recommendations. These recommendations are reviewed and revised on a regular basis based on new information that becomes available. If a debate occurs about a test being used for screening, it is usually because the evidence is not as clear or strong and is open to interpretation. One of the questions that may be answered is, "How many people have to be screened over a certain period of time, and at what cost, to save one life?" The answers to these questions help guide the recommendation. Sometimes the recommendations from one group differ from another. This can cause some confusion.
Should you have a screening test? It depends on a lot of factors. Age, gender, and known risk factors (family history, behaviors, or exposure to cancer-related agents) may influence a health care provider's recommendation for any individual. Other factors that may influence whether someone has a test include cost, access, and other concerns.
If screening tests are effective, people will be diagnosed with earlier stage cancers and deaths from those cancers will decline over time. In some cancers, like cervical and colorectal cancer, screening is achieving these goals. Greater benefits can be achieved if more people can be screened for these cancers. In other cancers, like lung cancer, progress needs to be made before there are more effective screening tools.