Screening tests are used to detect a disease before symptoms occur. Screening tests usually are not definitive. Results are confirmed or disproved with further examinations and tests.
Diagnostic tests are done once a doctor suspects that a person has cancer (see also Diagnosis of Cancer).
Some screening is conducted as part of routine physical examinations. Doctors do examinations that may indicate the presence of cancers of the thyroid, oral cavity, skin, lymph nodes, testes, prostate, cervix, and ovaries.
Doctors determine whether a particular person is at special risk of cancer—because of age, sex, family history, previous history, or lifestyle factors—before they choose to do screening tests. The American Cancer Society has provided cancer screening guidelines that are widely used. Other groups have also developed screening guidelines. Sometimes recommendations vary among different groups, depending on how each group's experts weigh the relative strength and importance of available scientific evidence.
Although screening tests can help save lives, test results can be falsely positive or falsely negative:
False-positive results: Results that suggest a cancer is present when it actually is not
False-negative results: Results that show no hint of a cancer that is actually present
False-positive results can create undue psychologic stress and can lead to other tests that are invasive or expensive. False-negative results can give a false sense of security, even though a person has a cancer. For these reasons, there are only a small number of screening tests that are considered reliable enough for doctors to use routinely.
In women, widely used screening tests are the Papanicolaou (Pap) test and tests for high-risk human papillomavirus (HPV) subtypes to detect cervical cancer and mammography to detect breast cancer. Screening tests for both breast and cervical cancer have been successful in reducing the death rates from these cancers in certain age groups. However, not all breast cancers that are found as a result of screening will go on to cause problems in a person's lifetime.
In men, prostate-specific antigen (PSA) levels in the blood may be used to screen for prostate cancer. PSA levels are often high in men with prostate cancer, but levels also are elevated in men with noncancerous (benign) enlargement of the prostate. As such, the main drawback to its use as a screening test is the large number of false-positive results, which generally lead to more invasive tests such as a prostate biopsy. Doctors also realize that not all prostate cancers found on biopsy will go on to cause problems during a person's lifetime. Whether the PSA test should be used routinely to screen for prostate cancer is unresolved, with varying recommendations from different groups. Men should discuss the PSA test with their doctor.
Several tests may be used to screen for colon cancer. People should discuss which test to use with their doctor. A common screening test for colon cancer involves checking the stool for blood that cannot be seen by the naked eye (occult blood). Finding occult blood in the stool is an indication that something is wrong somewhere in the digestive tract. The problem may be cancer, although many other disorders, such as ulcers, hemorrhoids, and abnormal blood vessels in the intestinal walls, can also cause small amounts of blood to leak into the stool. In addition, taking an aspirin or another nonsteroidal anti-inflammatory drug (NSAID) or even eating red meat can temporarily cause a positive test result. Another test checks for abnormal DNA in stool that has come from a colon cancer. Outpatient procedures such as sigmoidoscopy, colonoscopy, and a special type of computed tomography (CT) of the colon (CT colonography) are also often used for colon cancer screening.
Lung cancer screening with a lung CT is available for people between 50 and 80 years who currently smoke or quit smoking but have at least a 20-pack-year history of smoking. The risks and benefits of lung cancer screening should be discussed with a doctor.
Routine self-examination for signs of cancer has sometimes been recommended. However, except possibly for testicular cancer, home screening with self-examinations has not been proved to be effective in identifying cancer, so even if people do examinations at home it is important to also follow recommendations for screening tests.
Some screening tests can be done at home, such as checking the stool for blood by putting a small amount of stool on a special card and mailing it to a laboratory to be processed. An abnormal result should prompt a visit to the doctor for confirmation.
Tumor biomarkers are substances secreted into the bloodstream by certain tumors. It was first thought that measuring levels of these biomarkers would be an excellent way to screen for cancer in people who do not have symptoms. However, tumor biomarkers are often present to some extent in the blood of people who do not have cancer. Finding a tumor biomarker does not necessarily mean a person has cancer, and tumor biomarkers have a very limited role in cancer screening.
Cancer Screening Recommendations*
Procedure | Frequency |
|---|---|
Lung cancer | |
Low-dose computed tomography (CT) | Yearly in people between ages 50 and 80 years who smoke or who quit smoking and have at least a 20-pack-year history of smoking |
Colorectal cancer | |
Stool examination for occult blood or immunohistochemical test | Yearly from age 45 to 75† |
Stool DNA test | Multi-target stool DNA test every 3 years from age 45 to 75† |
Sigmoidoscopic or colonoscopic examination | Every 5 years from age 45 to 75† (sigmoidoscopy) Every 10 years from age 45 to 75† (colonoscopy) |
Computed tomography colonography | Every 5 years from age 45 to 75† |
Prostate cancer | |
Blood test for prostate-specific antigen (PSA) | The benefit of screening is uncertain, so men age 50 or older and their doctors should discuss the possible risks and benefits of screening African American men and men whose father or brother developed prostate cancer before age 65 should have this discussion at age 45 |
Cervical cancer | |
Papanicolaou (Pap) test and/or human papillomavirus (HPV) test | HPV test only or Pap test plus HPV test in women ages 25 to 65† Recommended starting age and frequency of screening varies from every 3 to 5 years depending on age, screening test, and medical organization guidelines |
Breast cancer | |
Mammography | Women ages 40–44: Option to start yearly screening Women ages 45–54: Yearly Women ≥ 55: Every 1–2 years; screening continues as long as woman is expected to live at least 10 more years |
* Recommendations for screening are influenced by many factors. These screening recommendations, based primarily on those of the American Cancer Society, are for people with an average risk of cancer who have no symptoms of cancer. For people with a higher risk, such as those with a strong family history of certain cancers or those who have had a previous cancer, screening may be recommended more frequently or to start at a younger age. Screening tests other than those listed here may also be recommended. Other organizations, such as the U.S. Preventive Services Task Force, may have slightly different recommendations, which are included here for some cancers. A person's physician can help the person decide when to begin screening and which tests should be used. | |
† Some screening recommendations include a starting age and stopping age. The decision to continue screening after the stopping age is based on a discussion with a doctor about the risks and benefits. | |
More Information
The following English-language resource may be useful. Please note that The Manual is not responsible for the content of this resource.
American Cancer Society: Cancer Screening Recommendations
