Results from research studies help doctors decide when a screening test works well enough to be used as a standard test.
Evidence about how safe, accurate, and useful cancerscreening tests are comes from clinical trials (research studies with people) and other kinds of research studies. When enough evidence has been collected to show that a screening test is safe, accurate, and useful, it becomes a standard test. Examples of cancer screening tests that were once under study but are now standard tests include:
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Different types of research studies are done to study cancer screening.
Cancer screening trials study new ways of finding cancer in people before they have symptoms. Screening trials also study screening tests that may find cancer earlier or are more accurate than existing tests, or that may be easier, safer, or cheaper to use. Screening trials are designed to find the possible benefits and possible harms of cancer screening tests. Different clinical trial designs are used to study cancer screening tests.
The strongest evidence about screening comes from research done in clinical trials. However, clinical trials cannot always be used to study questions about screening. Findings from other types of studies can give useful information about how safe, useful, and accurate cancer screening tests are.
The following types of studies are used to get information about cancer screening tests:
Randomized controlled trials
Randomizedcontrolled trials give the highest level of evidence about how safe, accurate, and useful cancer screening tests are. In these trials, volunteers are assigned randomly (by chance) to one of two or more groups. The people in one group (the control group) may be given a standard screening test (if one exists) or no screening test. The people in the other group(s) are given the new screening test(s). Test results for the groups are then compared to see if the new screening test works better than the standard test, and to see if there are any harmful side effects.
Using chance to assign people to groups means that the groups will probably be very much alike and that the trial results won't be affected by human choices or something else.
Nonrandomized controlled trials
In nonrandomized clinical trials, volunteers are not assigned randomly (by chance) to different groups. They choose which group they want to be in or the study leaders assign them. Evidence from this type of research is not as strong as evidence from randomized controlled trials.
A cohort study follows a large number of people over time. The people are divided into groups, called cohorts, based on whether or not they have had a certain treatment or been exposed to certain things. In cohort studies, the information is collected and studied after certain outcomes (such as cancer or death) have occurred. For example, a cohort study might follow a group of women who have regular Pap tests, and divide them into those who test positive for the human papillomavirus (HPV) and those who test negative for HPV. The cohort study would show how the cervical cancer rates are different for the two groups over time.