Cancer screening
Cancer screening tests asymptomatic average-risk adults at defined ages and intervals for breast, cervical, colorectal, and lung cancer, and earlier or more intensively in high-risk groups such as BRCA carriers, Lynch syndrome, and cirrhosis. A positive screen is not a diagnosis; every abnormal result requires a confirmatory diagnostic study before treatment decisions are made.
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What this article covers
- Overview
Definition: cancer screening applies a test to asymptomatic people to detect disease before it becomes clinically apparent, aiming to reduce cancer-specific mortality through earlier, more effective treatment.
- Epidemiology
Effectiveness is measured by disease-specific mortality, not survival: survival time is distorted by earlier diagnosis, so trials use mortality reduction as the outcome.
- Risk factors
Hereditary cancer syndromes: BRCA1/2 pathogenic variants confer a 50% to 85% lifetime risk of breast cancer; Lynch syndrome (mismatch repair genes MLH1, MSH2, MSH6, PMS2, or EPCAM) confers a 50% to 80% lifetime risk of colorectal cancer.
- Pathophysiology
Detectable preclinical phase: the window when disease is present and detectable but not yet symptomatic must be long enough for a test to catch it and short enough that disease has not already progressed.
- Clinical features
Screening applies only to the asymptomatic patient: anyone with a relevant symptom (unexplained bleeding, weight loss, a palpable mass, hemoptysis, jaundice) needs diagnostic evaluation, not a screening protocol.
- Differential diagnosis
Diagnostic testing for a symptomatic patient: ordered for a specific complaint (rectal bleeding, a palpable mass, hemoptysis) and proceeds directly to a definitive study, not a scheduled interval test.
- Diagnosis
Screening tests are applied against explicit age, interval, and threshold criteria for each cancer (given in Prevention below), and every positive screen requires confirmatory diagnostic testing…
- Management
First, confirm the patient is truly average-risk: family history, personal cancer history, pack-year smoking history, and cirrhosis status; any of these reclassifies the patient into a high-risk…
- Complications
False-positive results: the most common harm; 10-year cumulative false-positive rates with mammography reach roughly 42% with biennial screening starting at age 40.
- Prognosis
Strongest mortality-reduction evidence: colorectal, breast, cervical, and lung cancer screening each have controlled evidence for mortality reduction when done in the correct population at the correct interval.
- Prevention
Cervical cancer: cytology every 3 years from age 21; co-testing or primary HPV testing every 5 years from age 30 to 65; stop at 65 with adequate prior negative screening (three consecutive negative…
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