Some types of cancer can be found before they cause symptoms. Checking for cancer (or for conditions that may lead to cancer) in people who have no symptoms is called screening. Screening can help doctors find and treat some types of cancer early. Generally, cancer treatment is more effective when the disease is found early. However, not all types of cancer have screening tests and some tests are only for people with specific genetic risks.
Screening tests usually do not diagnose cancer. If a screening test result is abnormal, more tests may be done to check for cancer. For example, a screening mammogram may find a lump in the breast. A lump may be cancer or something else. More tests need to be done to find out if the lump is cancer. These are called diagnostic tests. Diagnostic tests may include a biopsy, in which cells or tissues are removed so a pathologist can check them under a microscope for signs of cancer.
Anything that increases the chance of cancer is called a cancer risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn’t mean that you will not get cancer.
Some screening tests are used only for people who have known risk factors for certain types of cancer. People known to have a higher risk of cancer than others include those who:
People who have a high risk of cancer may need to be screened more often or at an earlier age than other people.
Scientists are trying to better understand who is likely to get certain types of cancer. They study the things we do and the things around us to see if they cause cancer. This information helps doctors figure out who should be screened for cancer, which screening tests should be used, and how often the tests should be done.
Screening tests are used widely to check for cancers of the breast, cervix, colon, and rectum:
Breast: A mammogram is the best tool doctors have to find breast cancer early. A mammogram is a picture of the breast made with x-rays. The NCI recommends that women in their forties and older have mammograms every 1 to 2 years. Women who are at higher-than-average risk of breast cancer should talk with their health care provider about whether to have mammograms before age 40 and how often to have them.
Cervix: The Pap test (sometimes called Pap smear) is used to check cells from the cervix. The doctor scrapes a sample of cells from the cervix. A lab checks the cells for cancer or changes that may lead to cancer (including changes caused by human papillomavirus, the most important risk factor for cancer of the cervix). Women should begin having Pap tests 3 years after they begin having sexual intercourse, or when they reach age 21 (whichever comes first). Most women should have a Pap test at least once every 3 years.
Colon and rectum: A number of screening tests are used to detect polyps (growths), cancer, or other problems in the colon and rectum. People aged 50 and older should be screened. People who have a higher-than-average risk of cancer of the colon or rectum should talk with their doctor about whether to have screening tests before age 50 and how often to have them.
You may have heard about other tests to check for cancer in other parts of the body. At this time, we do not know whether routine screening with these other tests saves lives.