Scientists have developed, and continue to develop, tests that can be used to screen a person for cancer. Many people think that the main purpose of these screening tests is to look for cancer in people who don't have any signs of the disease or to find cancer in an early, easily treatable stage. But the true goals of cancer screening are to:

• lower the number of people who die from the disease, or eliminate deaths from cancer altogether
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• lower the number of people who develop the disease

Although some cancer screening tests have proven benefits that can help achieve these goals, others do not. When talking about cancer screening, it's important to understand that these tests can increase the apparent "cure rate" of a cancer, without actually affecting how many people die from the disease or the risk of dying from the disease. That's because sometimes cancer screening tests find cancer that isn't causing a person harm and won't cause a person harm in his or her lifetime.

One example is screening for prostate cancer. Due to the widespread increase in prostate cancer screening, the disease is being found in more men. However, many of these cancers do not pose a health threat. That's one reason why the number of deaths from prostate cancer today is still similar to what it was in 1975, even though the number of men who have been diagnosed with the disease and "cured" has gone up dramatically.

Because cancer screening tests can detect some tumors that don't need to be treated, improved cancer survival rates don't always mean that a test benefits everyone. In fact, the risks of having a screening test could outweigh the advantages. The best way to tell if a screening test has actual benefits, including a decrease in cancer deaths, is through randomized controlled clinical trials.

Screening benefits and risks

Deciding whether to have a screening test is not always as straightforward as it may seem. Screening has potential risks and benefits that a person should discuss with their doctor. The benefits include a potential decrease in the number of deaths from cancer. The risks include:

Overdiagnosis. Cancer screening tests may find slow-growing cancers that otherwise would not have been found or caused harm in a person's lifetime. The result is that a person may receive potentially harmful, painful, stressful, and/or expensive treatment that the person didn't need.

False positives. Sometimes a cancer screening test will suggest that a person has cancer when they do not.

Increased testing. Both overdiagnosis and false positives can lead to additional screening tests that a person may not need. These tests can be physically invasive, costly, and cause a person unnecessary stress and worry.

False reassurance. Sometimes a cancer screening test will suggest a person does not have cancer when they actually do. As a result, a person may not get needed treatment.

Screening test recommendations

Different organizations provide guidelines on cancer screening tests. Recommendations vary on which cancers people should have screening tests for, which screening tests should be used to screen for a particular cancer, and when and how often those tests should be done. It's important for people to talk to their doctors to determine which tests are appropriate for their age and medical history.

Two groups that provide screening test guidelines are the American Cancer Society (ACS) and the U.S. Preventive Services Task Force (USPSTF). Below is an overview of recommendations from both groups for common cancer screening tests for people without symptoms, but with risk factors for each type of cancer.

Breast cancer

Mammography. An x-ray of the breast.

• ACS recommendation: Women 40 and older should have one every year.
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• USPSTF recommendation: Women 40 to 75 years old should have one every one to two years.

Clinical breast examination. A breast examination performed by a medical professional.

• ACS recommendation: Women age 20 to 40 should have one every three years. Women 40 and older should have one every year.
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• USPSTF recommendation: There is not enough evidence to recommend this test by itself without mammography.

Breast self-examination. A breast examination performed by women on their own breasts.

• ACS recommendation: Women age 20 and older should perform one each month; the examination is considered "optional."
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• USPSTF recommendation: No recommendation.

Cervical cancer

Pap test. Cells are gently scraped from the outside of a woman's cervix and vagina and examined.

• ACS recommendation: Women should have a Pap test beginning three years after becoming sexually active or beginning at age 21. A standard Pap test should be done each year, or a liquid pap test can be done every two years.
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• USPSTF recommendation: Women age 18 to 65 should have a Pap test every one to three years.

Pelvic exam. A doctor examines a woman's vagina, cervix, uterus, fallopian tubes, ovaries, and (sometimes) the rectum.

• ACS recommendation: Women age 18 to 40 should have one every one to three years. Women 40 and older should have one every year.
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• USPSTF recommendation: No recommendation.

Colorectal cancer

The ACS recommends screening for colorectal cancer beginning at age 50 for both men and women using one of the tests mentioned below. The USPSTF recommends screening from the age of 50 to 75 with specific tests (see below). This group further recommends that adults between 76 and 85 should not have routine screening, because the risks outweigh the benefits, and that adults older than 85 can forgo colorectal cancer screening. It is important to talk with your doctor about colorectal cancer screening and the type of test and screening method that is best for your situation.

Common screening tests include:

Colonoscopy. This test checks the upper and lower part of the colon with a thin, lighted tube. The ACS and USPSTF recommend that men and women 50 and older have a colonoscopy every 10 years.

Fecal occult blood test (FOBT). This test is used to detect hidden blood in stool (feces). The ACS recommends that men and women 50 and older should have one every year, and the USPSTF recommends that men and women 50 and older should have a high-sensitivity test every year.

Sigmoidoscopy. This test checks the lower part of the colon with a thin, lighted tube. The ACS and USPSTF recommend that men and women 50 and older should have one every five years, preferably with a FOBT between sigmoidoscopy tests.

Digital rectal exam. In this test, a doctor inserts a gloved finger into the rectum to feel for anything abnormal. The ACS and USPSTF do not have recommendations for this test.

In addition, the USPSTF does not think there is enough evidence of benefit or harm to recommend virtual colonography and fecal DNA testing for regular colorectal cancer screening.

All tests that indicate an abnormality should be followed up with a colonoscopy.

Prostate cancer

Prostate-specific antigen (PSA) test. This blood test measures the level of a marker called PSA that may detect early prostate cancer. However, high PSA levels may also indicate conditions that are not cancer.

• ACS recommendation: Men 50 and older should be offered testing every year.
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• USPSTF recommendation: There is not enough evidence to recommend PSA testing in men.

Skin cancer

Complete skin examination. A doctor checks the skin for signs of skin cancer.

• ACS recommendation: Men and women should have one done periodically.
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• USPSTF recommendation: There is not enough evidence for or against skin examinations.

Conclusions

Screening for cancer has an understandable, intuitive appeal. Although cancer screening can potentially lower cancer deaths and the distress of cancer, it is important to remember that a person must weigh the potential risks and benefits for each screening test with their doctor. Some screening tests may be more appropriate for those who have a personal or family history of cancer or an inherited cancer-related syndrome. The best way to find the value of cancer screening tests is through randomized clinical trials.

More Information

Mammography-What to Expect

Pap Test-What to Expect

Digital Rectal Exam (DRE)-What to Expect

Sigmoidoscopy-What to Expect

Colonoscopy-What to Expect

Creative Ways to Promote Cancer Screening