Cancer Prevention, Detection, and Diagnosis: Screening, Risk, Tissue, and Staging
Screening versus diagnosis
Screening applies a test to asymptomatic, average-risk people; diagnosis confirms disease in symptomatic patients or those with abnormal screening. Know the major programs: colorectal screening from age 45 (colonoscopy or stool-based testing), biennial mammography from 40–74, cervical HPV-based testing beginning at 21–25, annual low-dose CT for lung cancer in adults 50–80 with at least 20 pack-years who currently smoke or quit within 15 years, and shared decision-making for PSA.
Risk and genetics
Separate population screening from high-risk surveillance (earlier or intensified breast MRI for BRCA carriers; colonoscopy every 1–2 years in Lynch syndrome). Germline testing is offered when personal or family history suggests hereditary predisposition. Somatic tumor profiling guides therapy but does not replace germline testing.
Tissue, grade, and stage
Tissue diagnosis is generally required. Grade describes differentiation; stage describes anatomic and biologic extent. TNM combines tumor size and invasion (T), nodes (N), and metastases (M), with separate clinical (cTNM), pathologic (pTNM), and post-neoadjuvant (ypTNM) classifications. Performance status is an independent prognostic factor.
Tumor markers
CA-125, CEA, CA 19-9, AFP, hCG, CA 15-3, and PSA are used mainly to monitor response and detect recurrence; only a few (AFP and hCG in germ cell tumors, PSA in prostate cancer) contribute to diagnosis or staging.
Worked example
A 62-year-old who smoked 30 pack-years and quit 3 years ago asks about lung screening. He meets criteria (age 50–80, at least 20 pack-years, quit within 15 years) for annual low-dose CT.
Traps: equating a rising tumor marker with relapse, treating on the basis of a marker without imaging or tissue confirmation, and confusing grade with stage.