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.ut it is important to keep in mind that screening tests can have potential harms as well as benefits. 1  Some screening tests may cause bleeding or other health problems. 2  Screening tests can have false-positive results—the test indicates that cancer may be present even though it is not. 3  Screening tests can have false-negative results—the test 4  ... Ove