Merck Manual

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Cancer Screening


Robert Peter Gale

, MD, PhD, Imperial College London

Last full review/revision Jul 2018| Content last modified Jul 2018
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Cancer can sometimes be detected in asymptomatic patients via regular physical examinations and screening tests. (See also Overview of Cancer.)

Physical examinations for cancers of the thyroid, oral cavity, skin, lymph nodes, testes, prostate, cervix, and ovaries should be a part of routine medical care.

Screening tests are tests that are done in asymptomatic patients at risk. The rationale is that early diagnosis may decrease cancer mortality by detecting cancer at an early and curable stage. Early detection may allow for less radical therapy and reduce costs. Risks include false-positive results, which necessitate confirmatory tests (eg, biopsy, endoscopy) that can lead to anxiety, significant morbidity, and significant costs; and false-negative results, which may give a mistaken sense of security, causing patients to ignore subsequent symptoms.

Screening for cancer should be done in the following circumstances:

  • When distinct high-risk groups can be identified (eg, people who have a strong family history of breast or prostate cancer)

  • When the disorder has an asymptomatic period during which treatment would alter outcome (breast cancer, colon cancer)

  • When the morbidity of the disorder is significant if detection is delayed

  • When a screening test is available that is sensitive, specific, and cost effective

Recommended screening schedules are constantly evolving based on ongoing studies (see table Screening Procedures in Average-Risk Asymptomatic People as Recommended by the American Cancer Society). Current considerations regarding screening include the developing understanding that some findings (particularly in prostate and breast tissues) that appear cancerous may not actually progress to cancer within a person's remaining lifetime. For example, routine screening for blood levels of prostate-specific antigen (PSA) in men and routine screening mammograms in women may result in biopsy findings that a pathologist considers a cancer but that will not manifest clinically as a cancer or that manifest as a cancer that does not adversely affect survival. In such cases, people may receive cancer treatments (eg, surgery, chemotherapy, radiation therapy) that do not benefit them.

The key issue in screening is how many people need to be screened to prevent one cancer death and how many people will receive unnecessary interventions. Because of these complexities, there is considerable controversy regarding who should be screened and at what ages for what cancers. We present recommendations from the American Cancer Society; recommendations from other professional organizations and scientific bodies (eg, the US Preventive Services Task Force [USPSTF]) may differ.


Screening Procedures in Average-Risk* Asymptomatic People as Recommended by the American Cancer Society

Type of Cancer





Women ages 40–44: Option to start annual screening

Women ages 45–54: Yearly

Women ≥ 55: Every 2 yr; screening continues as long as woman is in good health and expected to live at least 10 more yr

Cervical cancer

Papanicolaou (Pap) test sometimes with the human papillomavirus (HPV) test

Pap test every 3 yr between ages 21 and 29

Pap test plus HPV test every 5 yr between ages 30 and 65 or Pap test every 3 yr

After age 65, no testing if previous testing was done and results were normal

Prostate cancer

Blood test for prostate-specific antigen

Because the benefit of screening is uncertain, patient and physician should discuss the risks and possible benefits of prostate cancer screening beginning at age 50.

Rectal and colon cancer

Stool testing: Fecal occult blood, fecal immunochemical test, or stool DNA test


Yearly, starting at age 50 (every 3 yr for stool DNA test)

Flexible sigmoidoscopy


Every 5 yr, starting at age 50



Every 10 yr, starting at age 50

CT colonography

Every 5 yr, starting at age 50

*Patients at high-risk of certain cancers may need to be screened according to a different schedule.

Examinations for cancers of the thyroid, oral cavity, skin, lymph nodes, testes, and ovaries should also be done during routine medical care.

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