**Question:** All are recognised tumour markers except ?

A. Carcinoembryonic antigen (CEA)
B. Prostate-specific antigen (PSA)
C. Cancer antigen 125 (CA-125)
D. Alpha-fetoprotein (AFP)

**Core Concept:** A tumour marker is a substance that is produced in increased amounts during cancer development or progression, and can be detected in the bloodstream. In clinical practice, measuring these markers can help diagnose, monitor, or predict tumour response to treatment.

**Why the Correct Answer is Right:** AFP is a tumour marker that is typically elevated in the presence of liver or gastrointestinal cancers, such as hepatocellular carcinoma and neuroblastoma. However, it is not typically considered a "general" tumour marker like CEA, PSA, or CA-125.

**Why Each Wrong Option is Incorrect:**

A. CEA is a commonly used tumour marker for gastrointestinal and pancreatic cancers.
B. PSA is often increased in prostate cancer patients and can be used for monitoring treatment response.
C. CA-125 is mainly associated with ovarian cancer, but can also be elevated in other malignancies and conditions like endometriosis.

**Clinical Pearl:**

While tumour markers can provide valuable information in cancer diagnosis and management, they are not universally applicable to all cancers and should be interpreted in conjunction with clinical findings and other diagnostic tests.

**Correct Answer:** D. Alpha-fetoprotein (AFP)