Overdiagnosis

Overdiagnosis is the diagnosis of a condition that would never have caused symptoms or harm during a person's lifetime. It can lead to unnecessary treatment without benefiting the person.

Screening: The systematic testing of people without symptoms to identify disease or elevated risk. Screening can detect conditions that would never have become clinically important.
Breast cancer screening: The use of tests, especially mammography, to detect breast cancer before symptoms appear. Mammography can detect some breast cancers that would not have become harmful.
False positive: A test result that indicates a condition is present when it is not. Unlike overdiagnosis, a false positive is an erroneous result rather than a real, harmless condition.
Overdiagnosis rate: The proportion of diagnosed cases that would never have caused symptoms or harm during a person's lifetime. Its estimate depends on assumptions about what would have happened without diagnosis.
Lead-time bias: The apparent extension of survival time caused by diagnosing a disease earlier without delaying death. Earlier diagnosis can make survival after diagnosis look longer even when screening does not prevent death.
Prostate-specific antigen test: A blood test that measures prostate-specific antigen, a protein produced by prostate cells. PSA testing can uncover slow-growing prostate cancers that would never cause symptoms.
Incidental finding: A result discovered unexpectedly during testing performed for a different clinical question. Unexpected findings can prompt follow-up tests and diagnoses, including overdiagnosis.
Randomized controlled trial: A study that assigns participants randomly to interventions or comparison groups to estimate causal effects. Long-term comparisons of screened and unscreened groups can help estimate excess diagnoses.
Length-time bias: The tendency of screening to detect slower-progressing diseases more often than rapidly progressing ones. Screening disproportionately finds slow-growing abnormalities, some of which never cause harm.
Thyroid cancer screening: Testing people without symptoms for thyroid cancer, often through imaging or examination. Widespread imaging can find small thyroid cancers that would otherwise remain undetected.

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