The use of screening tests to detect cancers early often leads to more effective treatment with fewer side effects. Patients whose cancers are found early also are less likely to die from these cancers than are those whose cancers are not found until symptoms appear.

This section describes trends in the use of the following screening tests, each of which has been found to detect cancers accurately and to decrease the chances of dying from cancer:

• mammography (for breast cancer)
• pap smear (for cervical cancer)
• fecal occult blood test (for colorectal cancer)
• sigmoidoscopy (for colorectal cancer)

Trends for newer ways to detect cancer, such as the prostate specific antigen (PSA) test, may be included in future editions of the Cancer Progress Report. PSA use has not yet been proven to reduce deaths from prostate cancer. There is also concern about possible harm caused by unnecessary treatments, because the test can find very early cancers that might not cause any harm if left untreated— especially in older men. Other screening methods, such as new imaging techniques to detect lung cancer, or ways to detect early cancer in the blood, also require more research.