Checking for cancer (or for conditions 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. 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 is harder to treat.
Several screening tests have been shown to detect cancer early and to reduce the chance of dying from that cancer. These tests are described on the Screening Tests page.
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—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—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.
Overdiagnosis is possible. This happens when a 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.
What Is Cancer Screening?
- Cancer screening is looking for cancer before a person has any symptoms.
- There are different kinds of screening tests.
- Screening tests have risks.
- Some screening tests can cause serious problems.
- False-positive test results are possible.
- False-negative test results are possible.
- Finding the cancer may not improve the person’s health or help the person live longer.
Cancer screening is looking for cancer before a person has any symptoms.
Screening tests can help find cancer at an early stage, before symptoms appear. When abnormal tissue or cancer is found early, it may be easier to treat or cure. By the time symptoms appear, the cancer may have grown and spread. This can make the cancer harder to treat or cure.
It is important to remember that when your doctor suggests a screening test, it does not always mean he or she thinks you have cancer. Screening tests are done when you have no cancer symptoms.
There are different kinds of screening tests.
Screening tests include the following:
- Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
- Laboratory tests: Medical procedures that test samples of tissue, blood, urine, or other substances in the body.
- Imaging procedures: Procedures that make pictures of areas inside the body.
- Genetic tests: Tests that look for certain gene mutations (changes) that are linked to some types of cancer.
- Screening tests have risks.
Not all screening tests are helpful and most have risks. It is important to know the risks of the test and whether it has been proven to decrease the chance of dying from cancer.
Some screening tests can cause serious problems.
Some screening procedures can cause bleeding or other problems. For example, colon cancer screening with sigmoidoscopy or colonoscopy can cause tears in the lining of the colon.
False-positive test results are possible.
Screening test results may appear to be abnormal even though there is no cancer. A false-positive test result (one that shows there is cancer when there really isn’t) can cause anxiety and is usually followed by more tests and procedures, which also have risks.
False-negative test results are possible.
Screening test results may appear to be normal even though there is cancer. A person who receives a false-negative test result (one that shows there is no cancer when there really is) may delay seeking medical care even if there are symptoms.
Finding the cancer may not improve the person’s health or help the person live longer.
Some cancers never cause symptoms or become life-threatening, but if found by a screening test, the cancer may be treated. There is no way to know if treating the cancer would help the person live longer than if no treatment were given. In both teenagers and adults, there is an increased risk of suicide in the first year after being diagnosed with cancer. Also, treatments for cancer have side effects.
For some cancers, finding and treating the cancer early does not improve the chance of a cure or help the person live longer.
It can be helpful for people to discuss the potential harms as well as benefits of different cancer screening tests with their doctors.
Many cancer screening tests are in use. Some tests have been shown both to find cancer early and to lower the chance of dying from the disease. Others have been shown to find cancer early but have not been shown to reduce the risk of dying from cancer; however, they may still be offered to people, especially those who are known to be at increased risk of cancer.
- Screening Tests That Have Been Shown to Reduce Cancer Deaths
Colonoscopy, sigmoidoscopy, and high-sensitivity 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.
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.
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.