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Cancer Screening Overview

Does Screening Help People Live Longer?

Finding some cancers at an early stage (before symptoms appear) may help decrease the chance of dying from those cancers.

For many cancers, the chance of recovery depends on the stage (the amount or spread of cancer in the body) of the cancer when it was diagnosed. Cancers that are diagnosed at earlier stages are often easier to treat or cure.

Studies of cancer screening compare the death rate of people screened for a certain cancer with the death rate from that cancer in people who were not screened. Some screening tests have been shown to be helpful both in finding cancers early and in decreasing the chance of dying from those cancers. Other tests are used because they have been shown to find a certain type of cancer in some people before symptoms appear, but they have not been proven to decrease the risk of dying from that cancer. If a cancer is fast-growing and spreads quickly, finding it early may not help the person survive the cancer.

Screening studies are done to see whether deaths from cancer decrease when people are screened.

When collecting information on how long cancer patients live, some studies define survival as living 5 years after the diagnosis. This is often used to measure how well cancer treatments work. However, to see if screening tests are useful, studies usually look at whether deaths from the cancer decrease in people who were screened. Over time, signs that a cancer screening test is working include:

The number of deaths from cancer is lower today than it was in the past. It is not always clear if this is because screening tests found the cancers earlier or because cancer treatments have gotten better, or both. The Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute collects and reports information on survival times of people with cancer in the United States. This information is studied to see if finding cancer early affects how long these people live.

Certain factors may cause survival times to look like they are getting better when they are not.

These factors include lead-time bias and overdiagnosis.