# Tumour Markers

> Clinical use of AFP, CEA, CA-125, CA 19-9, PSA and beta-hCG tumour markers, with their limitations and pitfalls, for NEET-PG Medicine exam preparation.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/tumour-markers
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics; DeVita's Principles and Practice of Oncology; Harrison's Principles of Internal Medicine
- How to cite: "Tumour Markers", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/tumour-markers

## Direct answer

Tumour markers are substances in blood or tissue whose levels reflect malignancy, but most are neither sensitive nor specific enough to diagnose cancer alone. Their main roles are monitoring response and recurrence, and in a few tumours they help diagnosis: AFP in hepatocellular carcinoma and yolk sac tumour, beta-hCG in germ cell tumours and gestational trophoblastic disease, and PSA in prostate cancer. Benign causes of a raised level are often more common than cancer.

## What you must remember

- **AFP:** Hepatocellular carcinoma and yolk sac tumour; also raised in cirrhosis, hepatitis flares and pregnancy, so very high values are needed to favour cancer.
- **CEA:** Colorectal, gastric and lung adenocarcinoma; raised in smokers, inflammatory bowel disease and liver disease, and used for monitoring rather than screening.
- **CA-125:** Serous epithelial ovarian cancer; raised in endometriosis, fibroids, peritonitis and pelvic inflammation, so it is best used after a diagnosis is made.
- **CA 19-9:** Pancreatic adenocarcinoma; falsely raised in biliary obstruction and cholangitis, and absent in people who lack the Lewis antigen.
- **PSA:** Prostate-specific; falsely raised by prostatitis, catheterisation, recent biopsy and ejaculation, while 5-alpha reductase inhibitors lower it, so the reading is doubled after about six months of therapy.
- **beta-hCG:** Choriocarcinoma, gestational trophoblastic disease and germ cell tumours including seminoma with syncytiotrophoblasts; its half-life of roughly 24 to 36 hours makes it useful for tracking response, and pregnancy must always be excluded first.
- **LDH:** Not tumour specific, but a prognostic factor in germ cell tumours and lymphoma, and a marker of tumour burden.

## Worked scenario: a rising PSA in a 62-year-old man

A 62-year-old man is referred with a PSA rising from 4 to 9 ng/mL over a year. The steps show how the reading is made reliable before any biopsy is considered.

1. **Check the reading is reliable:** Ask whether he was catheterised, has had a recent biopsy or infection, has taken finasteride, or ejaculated before the sample.
2. **Treat and repeat:** A urinary infection or prostatitis is treated and the test repeated after a pause, rather than moving to biopsy.
3. **Examine the ratio:** If the rise persists, the free-to-total PSA ratio is examined, because a low ratio favours cancer over benign enlargement.
4. **Image before biopsy:** Multiparametric MRI guides targeted biopsy, and the marker is interpreted as a trend, not a single number.

| Marker | Main association | Commonest pitfall |
|---|---|---|
| AFP | Hepatocellular carcinoma, yolk sac tumour | Raised in cirrhosis, hepatitis and pregnancy |
| CEA | Colorectal, gastric and lung adenocarcinoma | Raised in smokers and inflammatory bowel disease |
| CA-125 | Serous epithelial ovarian cancer | Raised in endometriosis, fibroids and peritonitis |
| CA 19-9 | Pancreatic adenocarcinoma | Falsely raised in biliary obstruction |
| PSA | Prostate cancer | Raised by prostatitis, lowered by 5-alpha reductase inhibitors |
| beta-hCG | Germ cell tumours and choriocarcinoma | Pregnancy must be excluded first |

The reasoning shows that a tumour marker is only as good as the context in which it is measured.

## Where the examiner tests the limits

Marker questions usually test a limit of the marker rather than its definition.

- **Trap:** using a marker as a screening test. — **Correct:** CEA is not used to screen for colorectal cancer, and CA-125 is not a screening tool for ovarian cancer in the average woman, because benign causes are frequent.
- **Trap:** reading a PSA of 3 at face value on finasteride. — **Correct:** a man on a 5-alpha reductase inhibitor has the value doubled before interpretation.
- **Trap:** ignoring the beta-hCG half-life. — **Correct:** a half-life of roughly 24 to 36 hours lets clinicians judge whether a germ cell tumour is responding.
- **Trap:** choosing the wrong set of germ cell markers. — **Correct:** the expected set is AFP, beta-hCG and LDH.

## Frequently asked questions

### Which tumour markers are used to monitor germ cell tumours?

AFP, beta-hCG and LDH monitor germ cell tumours and contribute to staging. Seminoma may raise beta-hCG and LDH but not AFP, which helps distinguish histological types.

### Why is CEA not used for colorectal cancer screening?

CEA lacks the sensitivity and specificity needed for population screening, since many early colorectal cancers do not raise it and smokers often have raised values. Colorectal screening relies on stool-based tests or colonoscopy instead.

### Which benign conditions raise CA-125 levels?

Endometriosis, uterine fibroids, pelvic inflammatory disease, peritonitis and cirrhosis can all raise CA-125. Its value lies in monitoring known serous epithelial ovarian cancer rather than in diagnosis.

### How does finasteride affect PSA interpretation?

Finasteride, a 5-alpha reductase inhibitor, lowers serum PSA by roughly half after several months of therapy. The usual approach is to double the measured PSA after about six months on the drug before interpreting it.

### What is the half-life of beta-hCG and why does it matter?

The half-life of beta-hCG is roughly 24 to 36 hours, much shorter than that of AFP. This lets clinicians track whether a gestational trophoblastic or germ cell tumour is responding in weeks rather than months. Pregnancy must be excluded before a raised value is attributed to a tumour.