Key Messages:

• The goal of cancer screening is to lower the number of people who develop and die from cancer.
  
  
• Talk with your doctor about which screening tests are right for you and the benefits and risks of a particular test.

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 overall goals of cancer screening are to:

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

Not all screening tests beneficial

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. Because of 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 (research studies in people).

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 talk about with his or her doctor, especially in the context of a his or her personal and family medical history. 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 cancer 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.

Breast cancer

Mammography. An x-ray of the breast.

• ACS recommendation: Women 40 and older should have one every year.
  
  
• USPSTF recommendation: Women 50 to 74 years old should have one every two years. There is not enough evidence to assess the additional harms and benefits of mammography for women 75 and older.

Read ASCO’s perspective on mammography screening for breast cancer and what to expect during a mammography.

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

• ACS recommendation: Women 20 to 40 years old should have one every three years. Women 40 and older should have one every year.
  
  
• USPSTF recommendation: The current evidence is insufficient to assess the additional benefits and harms of clinical breast examination beyond screening mammography in women 40 years or older.

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

• ACS recommendation: Women 20 and older should perform one each month; the examination is considered "optional."
  
  
• USPSTF recommendation: Recommends against teaching breast self-examination.

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.
  
  
• USPSTF recommendation: Women 18 to 65 years old should have a Pap test every one to three years.

In November 2009, the American College of Obstetricians and Gynecologists recommended that women younger than 30 have a Pap test every two years and those 30 and older, every three years. Some groups may change their recommendations based on this information. Talk with your doctor for more information and read ASCO’s statement on breast and cervical cancer screening.

Read what to expect during a Pap test.

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

• ACS recommendation: Women 18 to 40 years old should have one every one to three years. Women 40 and older should have one every year.
  
  
• 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). USPSTF 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.

Read what to expect during a colonoscopy.

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.

Read what to expect during a fecal occult blood test.

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.

Read what to expect during a sigmoidoscopy.

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.

Read what to expect during a digital rectal exam.

In addition, the USPSTF does not think there is enough evidence of benefit or harm to recommend virtual colonography (also known as virtual colonoscopy) 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.
  
  
• USPSTF recommendation: There is not enough evidence to recommend PSA testing in men.

Read more about the benefits and risks of PSA testing.

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.
  
  
• 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

Risk Factors and Prevention

Last Updated: November 30, 2009