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Tumor Markers of Cancer
As described in Robbins Pathology
Definition
Tumor markers are biochemical assays for tumor-associated enzymes, hormones, and other substances detectable in blood or other body fluids. They cannot be used for definitive diagnosis of cancer because they lack the sensitivity and specificity needed for that purpose. However, in concert with other investigations, they contribute to:
- Detection/screening of certain cancers (with limitations)
- Monitoring response to therapy
- Detecting tumor recurrence
(Robbins, Cotran & Kumar - Pathologic Basis of Disease)
Important Limitations
All tumor markers share common limitations, well illustrated by PSA (the most widely studied):
- Low specificity - Elevated in benign conditions (e.g., PSA raised in benign prostatic hyperplasia)
- Low sensitivity - Cancer may be present even with normal marker levels
- Not diagnostic alone - Must always be combined with clinical findings, imaging, and biopsy
With successful tumor resection, markers disappear from serum. Their persistence or reappearance almost always indicates residual or recurrent tumor - this is their most clinically reliable use.
Classification of Tumor Markers (Table 7.12, Robbins Pathologic Basis of Disease)
1. Hormones
| Marker | Associated Tumor |
|---|---|
| Human Chorionic Gonadotropin (hCG) | Trophoblastic tumors, non-seminomatous testicular germ cell tumors |
| Calcitonin | Medullary carcinoma of thyroid |
| Catecholamines and metabolites (VMA, metanephrines) | Pheochromocytoma and related tumors |
| Ectopic hormones (e.g., ACTH, PTHrP) | Various paraneoplastic syndromes |
2. Oncofetal Antigens
These are antigens normally expressed during fetal development and re-expressed by tumors:
a. Alpha-Fetoprotein (AFP)
- Produced by hepatocellular carcinoma (HCC), yolk sac tumors, and occasionally teratocarcinomas and embryonal cell carcinomas
- Also elevated in non-neoplastic conditions: cirrhosis, hepatitis, pregnancy - limiting its screening value
- Useful for monitoring response to therapy and detecting recurrence
b. Carcinoembryonic Antigen (CEA)
- Elaborated by carcinomas of the colon, pancreas, stomach, lung, and breast
- Elevated in many benign conditions: inflammatory bowel disease, pancreatitis, hepatitis, cirrhosis, heavy smoking
- Primary use: monitoring colorectal cancer treatment and detecting recurrence
- Not reliable as a primary screening tool
3. Lineage-Specific Proteins
| Marker | Associated Tumor |
|---|---|
| Immunoglobulins (monoclonal Ig / M protein) | Multiple myeloma, Waldenstrom macroglobulinemia, other secretory plasma cell tumors |
| Prostate-Specific Antigen (PSA) and Prostate-Specific Membrane Antigen (PSMA) | Prostate adenocarcinoma |
PSA in detail:
- Most frequently used tumor marker in clinical practice
- Elevated levels raise suspicion for prostatic carcinoma
- Also elevated in benign prostatic hyperplasia (BPH) and prostatitis
- Prostate cancer can exist even with PSA in the normal range
- Extremely valuable for detecting residual disease or recurrence following treatment
4. Mucins and Other Glycoproteins (Cancer Antigens - CA)
| Marker | Associated Tumor |
|---|---|
| CA-125 | Ovarian cancer (also fallopian tube, colon cancer); elevated in benign conditions (endometriosis, pelvic inflammatory disease, pregnancy) |
| CA-19-9 | Colorectal cancer, pancreatic cancer; also gastrointestinal and hepatobiliary cancers |
| CA-15-3 | Breast cancer |
5. Cell-Free DNA Markers ("Liquid Biopsy")
| Marker | Associated Tumor |
|---|---|
| EGFR mutants in serum | Lung cancer |
| TP53, APC, RAS mutants in stool and serum | Colon cancer |
These represent an emerging category where circulating tumor DNA (ctDNA) shed by tumors into blood or stool is detected. This "liquid biopsy" approach is increasingly used for:
- Early cancer detection
- Monitoring treatment response
- Detecting minimal residual disease (MRD)
Other Specific Markers Mentioned in Robbins
| Marker | Associated Tumor | Notes |
|---|---|---|
| Neuron-Specific Enolase (NSE) | Small cell lung carcinoma, neuroblastoma | Neuroendocrine marker |
| Thyroglobulin | Thyroid follicular/papillary carcinoma | Used post-thyroidectomy to detect recurrence |
| Placental alkaline phosphatase (PALP) | Seminoma | |
| Lactate Dehydrogenase (LDH) | Lymphomas, testicular tumors, dysgerminoma | Non-specific but prognostic value |
Clinical Uses Summarized
| Use | Comment |
|---|---|
| Screening | Limited - most markers lack sufficient specificity (PSA most studied) |
| Diagnosis | Cannot diagnose cancer on their own; supportive role |
| Staging | Some markers (e.g., AFP, hCG in testicular cancer) contribute to staging |
| Monitoring therapy | Most important use - fall with successful treatment |
| Detecting recurrence | Rise after remission = strong indicator of recurrence |
| Detecting minimal residual disease | Especially molecular markers (BCR-ABL, ctDNA) |
Key Points (Robbins)
- Tumor markers are not sensitive or specific enough to diagnose cancer alone
- Their greatest value is in monitoring therapy and detecting recurrence
- PSA, CEA, AFP, CA-125, CA-19-9 are the most widely used in clinical practice
- Cell-free DNA and liquid biopsy approaches represent the newest frontier
- Benign conditions can elevate virtually every tumor marker - always interpret in clinical context
Sources: Robbins, Cotran & Kumar - Pathologic Basis of Disease (10th ed.), Table 7.12 and surrounding text; Robbins & Kumar Basic Pathology (Robbins Pathology)
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