Checking for cancer (or for abnormal cells that may become cancer) in people who have no symptoms is called screening.
Screening can help doctors find and treat several types of cancer early, before they cause symptoms. Early detection is important because when abnormal tissue or cancer is found early, it may be easier to treat. By the time symptoms appear, cancer may have begun to spread and be harder to treat.
Several screening tests have been shown to detect cancer early and to reduce the chance of dying from that cancer.
But it is important to keep in mind that screening tests can have potential harms as well as benefits:
- Some screening tests may cause bleeding or other health problems.
- Screening tests can have false-positive results, that is, the test indicates that cancer may be present even though it is not. False-positive test results can cause anxiety and are usually followed by additional tests and procedures that also have potential harms.
- Screening tests can have false-negative results, that is, the test indicates that cancer is not present even though it is. False-negative test results may provide false reassurance, leading to delays in diagnosis and possibly causing an individual to put off seeking medical care even if symptoms develop.
- Screening can lead to overdiagnosis, that is, the screening test correctly shows that a person has cancer, but the cancer is slow growing and would not have harmed that person in his or her lifetime. Treatment of such cancers is called overtreatment.
Screening Tests that have been shown to reduce Cancer Deaths
Colonoscopy, Sigmoidoscopy, and Fecal Occult Blood Tests (FOBTs)
These tests have all been shown to reduce deaths from colorectal cancer. Colonoscopy and sigmoidoscopy also help prevent colorectal cancer because they can detect abnormal colon growths (polyps) that can be removed before they develop into cancer. Expert groups generally recommend that people who are at average risk for colorectal cancer have screening at ages 50 through 75.
Low-dose Helical Computed Tomography
This test to screen for lung cancer has been shown to reduce lung cancer deaths among heavy smokers ages 55 to 74.
This method to screen for breast cancer has been shown to reduce mortality from the disease among women ages 40 to 74, especially those age 50 or older.
Pap Test and Human Papillomavirus (HPV) testing
These tests reduce the incidence of cervical cancer because they allow abnormal cells to be identified and treated before they become cancer. They also reduce deaths from cervical cancer. Testing is generally recommended to begin at age 21 and to end at age 65, as long as recent results have been normal.
Other Screening Tests
Alpha-fetoprotein Blood Test
This test is sometimes used, along with ultrasound of the liver, to try to detect liver cancer early in people at high risk of the disease.
This imaging test is often used for women who carry a harmful mutation in the BRCA1 gene or the BRCA2 gene; such women have a high risk of breast cancer, as well as increased risk for other cancers.
CA 125 Test
This blood test, which is often done together with a transvaginal ultrasound, may be used to try to detect ovarian cancer early, especially in women with an increased risk of the disease. Although this test can help in diagnosing ovarian cancer in women who have symptoms and can be used to evaluate the recurrence of cancer in women previously diagnosed with the disease, it has not been shown to be an effective ovarian cancer screening test.
Clinical Breast Exams and regular Breast Self-Exams
Routine examination of the breasts by health care providers or by women themselves has not been shown to reduce deaths from breast cancer. However, if a woman or her health care provider notices a lump or other unusual change in the breast, it is important to get it checked out.
This blood test, which is often done along with a digital rectal exam, is able to detect prostate cancer at an early stage. However, expert groups no longer recommend routine PSA testing for most men because studies have shown that it has little or no effect on prostate cancer deaths and leads to overdiagnosis and overtreatment.
Doctors often recommend that people who are at risk for skin cancer examine their skin regularly or have a health care provider do so. Such exams have not been shown to decrease the risk of dying from skin cancer, and they may lead to overtreatment. However, people should be aware of changes in their skin, such as a new mole or a change to an existing mole, and report these to their doctor promptly.
This imaging test, which can create pictures of a woman’s ovaries and uterus, is sometimes used in women who are at increased risk of ovarian cancer (because they carry a harmful BRCA1 or BRCA2 mutation) or of endometrial cancer (because they have a condition called Lynch syndrome). But it has not been shown to reduce deaths from either cancer.
This test allows the colon and rectum to be examined from outside the body. However, it has not been shown to reduce deaths from colorectal cancer.