Tumour Markers Overview
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Direct answer
Molecules produced by a tumour — or by the host responding to it — and measurable in blood or tissue are tumour markers, and their honest role is monitoring response, detecting recurrence and estimating burden, far more than screening or diagnosis, because benign conditions elevate nearly every marker. The exam-worthy set runs: alpha-fetoprotein for hepatocellular carcinoma and yolk sac tumours, CEA for colorectal cancer follow-up, CA 125 for ovarian epithelial cancer, CA 19-9 for pancreaticobiliary tracking, PSA for prostate disease (organ-specific, not cancer-specific), beta-hCG for trophoblastic and germ cell tumours, and calcitonin for medullary thyroid carcinoma. Questions almost always pair a marker with its disease or, more sneakily, with its false-positive condition.
What you must remember
- Oncofoetal pair: AFP (raised in hepatocellular carcinoma — a level above 400 ng/mL with a liver mass is essentially diagnostic in cirrhotics — and yolk sac tumours) and CEA (colorectal, pancreatic and breast cancers; also smokers, liver disease, inflammatory bowel disease).
- Gynaecological set: CA 125 for epithelial ovarian cancer monitoring — false-raised in endometriosis, pregnancy, fibroids, ascites and even heart failure; inhibin for granulosa cell tumour; HE4 as an adjunct.
- Pancreaticobiliary: CA 19-9 for monitoring pancreatic adenocarcinoma; it is undetectable in Lewis antigen-negative individuals (about 5 per cent), and rises with any biliary obstruction.
- Prostate caution: PSA is organ-specific, not cancer-specific — benign hyperplasia, prostatitis and instrumentation all elevate it; the free-to-total ratio improves discrimination in the grey zone of 4-10 ng/mL.
- Germ cell pair: beta-hCG from syncytiotrophoblasts (choriocarcinoma, some testicular seminomas) and AFP from yolk sac elements — together they stage and monitor non-seminomatous germ cell tumours, with LDH as the third marker of burden.
- Endocrine markers: calcitonin (medullary thyroid carcinoma, RET screening) and thyroglobulin (post-thyroidectomy surveillance of differentiated thyroid cancer, invalid if anti-thyroglobulin antibodies present).
- Haematological adjuncts: serum M-protein and free light chains for myeloma, beta-2 microglobulin as its prognostic marker, and chromogranin for neuroendocrine tumours.
Monitoring, not guessing, in clinic
A woman operated for stage III ovarian cancer has a CA 125 of 35 U/mL before chemotherapy that falls to 8 after three cycles — a marker trajectory confirming response, exactly the use markers are built for. Six months later it climbs to 90 while she feels well: recurrence is searched for radiologically, because a rising marker without symptoms still defines biochemical relapse in trophoblastic and germ cell disease, where treatment can begin on marker criteria alone. Contrast the wrong use: screening asymptomatic women with CA 125 generates false positives from endometriosis and fibroids, and screening smokers with CEA detects nothing useful early. The disciplined sentence for any viva — markers monitor, histology diagnoses — is also the safest clinical habit.
Where students slip
Single-best-answer papers love the false-positive angle: ascites raising CA 125, biliary obstruction raising CA 19-9, prostatitis raising PSA, pregnancy raising both beta-hCG and AFP. The Lewis antigen nuance of CA 19-9 appears regularly — a patient who cannot synthesise the antigen will never produce the marker. Students also forget that seminoma can produce beta-hCG (from syncytiotrophoblastic giant cells) but never AFP, and that AFP-producing tumours in a young man with a retroperitoneal mass mean non-seminomatous disease, changing chemotherapy.
Frequently asked questions
Which marker monitors epithelial ovarian cancer?
CA 125, with the caveat that endometriosis, pregnancy, fibroids and ascites raise it in the absence of cancer.
What is the diagnostic AFP level for hepatocellular carcinoma?
A level above 400 ng/mL in a cirrhotic patient with a liver mass is considered diagnostic without biopsy; lower levels require imaging surveillance interpretation.
Why can CA 19-9 be normal in pancreatic cancer?
Individuals negative for the Lewis antigen (roughly 5 per cent) cannot synthesise the CA 19-9 epitope, so their tumours never secrete it.
Which markers are used in testicular germ cell tumours?
AFP from yolk sac elements, beta-hCG from syncytiotrophoblasts and LDH for tumour burden — together they stage, choose therapy and monitor.
Which marker screens families for medullary thyroid carcinoma?
Calcitonin, with RET proto-oncogene testing, since medullary carcinoma arises from calcitonin-secreting parafollicular C cells.