Cancer screening tests aim to find cancer early, before it causes symptoms and when it may be easier to treat successfully. Effective screening tests are those that:

• Find cancer early

• Reduce the chance that someone who is screened regularly will die from the cancer

• Have more potential benefits than harms. (Possible harms of screening tests include bleeding or other physical damage, inaccurate test results, and overdiagnosis—the diagnosis of cancers that would not have caused problems and did not need treatment.)