Tumor Markers - Cancer's Calling Cards
- Substances (proteins, enzymes, hormones, oncofetal antigens, genetic changes) produced by tumor cells or by the body in response to cancer.
- Ideal Characteristics:
- High sensitivity & specificity for a single cancer.
- Levels correlate with tumor burden & prognosis.
- Early detection capability.
- Cost-effective & easy to measure.
- Classification:
- Enzymes & Isoenzymes: PSA, LDH, ALP.
- Hormones: HCG, Calcitonin, ADH, Gastrin.
- Oncofetal Antigens: AFP, CEA.
- Carbohydrate Markers: CA 125, CA 19-9, CA 15-3.
- Proteins: Monoclonal immunoglobulins (Bence Jones proteins).
- Genetic Markers: BRCA1/2, HER2/neu, EGFR.
⭐ AFP (Alpha-fetoprotein) is a marker for Hepatocellular Carcinoma and non-seminomatous germ cell tumors (e.g., Yolk Sac Tumor).
Markers & Matches - Rogues' Gallery
| Marker | Primary Association(s) | Key Notes |
|---|---|---|
| AFP | HCC, Yolk Sac Tumor | ↑ NTDs, pregnancy. Monitor GCT response. |
| β-hCG | Choriocarcinoma, Mole, GCTs | ↑ pregnancy. Monitor GCTs, trophoblastic disease. |
| CA 19-9 | Pancreatic Ca, Cholangiocarcinoma | Lewis Ag (-ve) no production. ↑ benign GI. |
| CA 125 | Ovarian Ca (epithelial) | Monitor. ↑ endometriosis, PID, pregnancy. |
| CA 15-3/27.29 | Breast Ca | Monitor recurrence. Not for screening. |
| CEA | Colorectal Ca (CRC) | Monitor recurrence/prognosis. ↑ other adenoCa, smokers. |
| PSA | Prostate Ca | Screen & monitor. ↑ BPH, prostatitis. %free PSA aids. |
| Calcitonin | Medullary Thyroid Ca (MTC) | From C-cells. MEN2. Pentagastrin test. |
| Chromogranin A | Neuroendocrine Tumors (NETs) | Carcinoid, Pheochromocytoma. General NET marker. |
| LDH | GCTs, Lymphoma, Leukemia | Non-specific. Tumor burden, prognosis. |
| Thyroglobulin | Papillary/Follicular Thyroid Ca | Monitor post-thyroidectomy. Check anti-Tg Ab. |
| S-100 | Melanoma, Schwannoma, Histiocytosis | Neural crest origin. |
| NSE | SCLC, Neuroblastoma | Neuroendocrine marker. Prognostic. |
| HER2/neu | Breast Ca, Gastric Ca | Oncogene (c-erbB2). Target: Trastuzumab. |
| CD20 | B-cell Lymphomas (most NHL) | Target: Rituximab. |
| CD30 | Hodgkin Lymphoma (RS cells), ALCL | Reed-Sternberg cells. |
| BRAF V600E | Melanoma, Papillary Thyroid Ca, Hairy Cell Leukemia | Mutation. Target: Vemurafenib. |
| BCR-ABL | CML | Philadelphia t(9;22). Target: Imatinib. |
| ALK | Lung Adenocarcinoma, ALCL | Rearrangement. Target: Crizotinib. |
| ER/PR | Breast Cancer | Hormone receptors. Predicts endocrine therapy response. |
Clinical Utility - Detective Work
- Screening:
- Limited in asymptomatic (low sensitivity/specificity).
- Uses: PSA (prostate risk), AFP (HCC surveillance).
- Diagnosis:
- Aids differential; rarely definitive. Context crucial.
- E.g., ↑ hCG/AFP strongly suggest testicular GCTs.
- Prognosis/Staging:
- Levels correlate with burden, stage, prognosis.
- E.g., CA-125 (ovarian), CEA (colorectal).
- Monitoring Therapy & Recurrence:
- Primary value: Serial levels track efficacy; ↑ suggests recurrence.
- ↑ levels often predate clinical/radiological signs (CEA, CA 15-3).
- Limitations:
- False Positives: Benign conditions (inflammation, organ failure).
- False Negatives: Non-secreting tumors or very low levels.
- Heterogeneous tumor expression.
⭐ Key role: Monitor therapy/recurrence, not primary screening/diagnosis.
High‑Yield Points - ⚡ Biggest Takeaways
- AFP: ↑ in hepatocellular carcinoma, yolk sac tumors.
- β-hCG: ↑ in choriocarcinoma, testicular germ cell tumors.
- CA 19-9: Marker for pancreatic cancer, also cholangiocarcinoma.
- CA-125: Monitors ovarian cancer (especially surface epithelial).
- CEA: For colorectal cancer recurrence; also some GI, lung cancers.
- PSA: Key for prostate cancer screening and monitoring.
- Calcitonin: Diagnostic for medullary thyroid carcinoma.
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