tumor marker
Summary
Tumor markers are biomolecules (proteins, hormones, enzymes, or antigens) produced by cancer cells or by the body in response to cancer, used for screening, diagnosis, prognosis, monitoring treatment response, and detecting recurrence. They are generally not used alone for definitive diagnosis due to limited sensitivity/specificity, but are high-yield for boards as classic associations with specific malignancies.
Detail
Tumor markers are substances found in blood, urine, or tissue that can be elevated in the presence of certain cancers. They arise either from tumor cells directly (e.g., secreted antigens) or as a host response to tumor presence. Key clinical uses include: (1) screening in high-risk populations (limited, e.g., AFP in hepatocellular carcinoma surveillance in cirrhotics), (2) aiding diagnosis when combined with imaging/biopsy, (3) prognostic stratification, (4) monitoring response to therapy, and (5) detecting recurrence after treatment. High-yield tumor markers for USMLE include: AFP (hepatocellular carcinoma, yolk sac/nonseminomatous germ cell tumors), CA-125 (ovarian cancer), CA 19-9 (pancreatic cancer), CEA (colorectal cancer, nonspecific), PSA (prostate cancer, screening controversial due to false positives from BPH/prostatitis), beta-hCG (choriocarcinoma, gestational trophoblastic disease, germ cell tumors), CA 15-3/CA 27-29 (breast cancer monitoring), calcitonin (medullary thyroid carcinoma, associated with MEN2), chromogranin A (neuroendocrine tumors), S-100 (melanoma, neural tumors), and Bence Jones protein (multiple myeloma light chains). Importantly, most tumor markers lack sufficient sensitivity and specificity for population-based screening (exception: possibly AFP in high-risk cirrhotic patients and PSA in select scenarios) because they can be elevated in benign conditions (e.g., CEA in smokers, CA-125 in endometriosis) or absent in early-stage cancers. Their greatest utility is in monitoring known cancers for recurrence after establishing a baseline post-treatment level.
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- Goljan Rapid Review Pathology
- UpToDate: Tumor Markers
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