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.

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.
  • Fecal occult blood test: Sometimes cancer or polyps bleed. This test can detect tiny amounts of blood in the stool.
  • Sigmoidoscopy: The doctor checks inside the rectum and lower part of the colon with a lighted tube called a sigmoidoscope. The doctor can usually remove polyps through the tube.
  • Colonoscopy: The doctor examines inside the rectum and entire colon using a long, lighted tube called a colonoscope. The doctor can usually remove polyps through the tube.
  • Double-contrast barium enema: This procedure involves several x-rays of the colon and rectum. The patient is given an enema with a barium solution, and air is pumped into the rectum. The barium and air improve the x-ray images of the colon and rectum.
  • Digital rectal exam: A rectal exam is often part of a routine physical exam. The health care provider inserts a lubricated, gloved finger into the rectum to feel for abnormal areas. A digital rectal exam allows for examination of only the lowest part of the rectum.

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. The NCI is supporting research to learn more about screening for cancers of the breast, cervix, colon, lung, ovary, prostate, and skin. See "The Promise of Cancer Research" section.

Doctors consider many factors before they suggest a screening test. They weigh factors related to the test and to the cancer that the test can detect. They also pay special attention to a person's risk for developing certain types of cancer. For example, doctors think about the person's age, medical history, general health, family history, and lifestyle. They consider how accurate the test is. In addition, doctors keep in mind the possible harms of the screening test itself. They also look at the risk of follow-up tests or surgery that the person might need to see if an abnormal test result means cancer. Doctors also think about the risks and benefits of treatment if testing finds cancer. They consider how well the treatment works and what side effects it causes.

You may want to talk with your doctor about the possible benefits and harms of being checked for cancer. The decision to be screened, like many other medical decisions, is a personal one. Each person should decide after learning about the pros and cons of screening.

The NCI has several fact sheets about screening tests. See the "National Cancer Institute Publications" section to learn how to get fact sheets.

You may want to ask the doctor the following questions about screening:

• Which tests do you recommend for me? Why?
• How much do the tests cost? Will my health insurance help pay for screening tests?
• Do the tests hurt? Are there any risks?
• How soon after the tests will I learn the results?
• If the results show a problem, how will you learn if I have cancer?