**Question:** Tumour marker for choriocarcinoma is -

A. Carcinoembryonic antigen (CEA)
B. Cancer antigen 125 (CA-125)
C. Human chorionic gonadotropin (hCG)
D. Alpha-fetoprotein (AFP)

**Correct Answer:** C. Human chorionic gonadotropin (hCG)

**Core Concept:** Tumour markers are substances that increase or decrease in the bloodstream when certain types of tumours are present. In the context of choriocarcinoma, we are looking for a marker that is elevated due to the presence of this specific type of cancer.

**Why the Correct Answer is Right:** Human chorionic gonadotropin (hCG) is a protein hormone that plays a crucial role in pregnancy. In non-pregnant individuals, hCG levels remain undetectable or very low. When choriocarcinoma, a type of gestational trophoblastic disease, develops, the tumour cells produce and release hCG into the bloodstream. This leads to elevated hCG levels, which can be detected in blood tests. Elevated hCG levels help in diagnosing choriocarcinoma and monitoring its response to treatment.

**Why Each Wrong Option is Incorrect:**

A. Carcinoembryonic antigen (CEA) is a tumor marker that is raised in patients with gastrointestinal malignancies, particularly colorectal cancer. It is not specific to choriocarcinoma and thus is not the correct marker for this tumour type.

B. Cancer antigen 125 (CA-125) is a marker associated with ovarian cancer and not specific to choriocarcinoma. It is not the correct marker for this tumour type.

D. Alpha-fetoprotein (AFP) is a marker associated with germ cell tumours, particularly in testicular cancer, but not specifically with choriocarcinoma. It is not the correct marker for this tumour type.

**Clinical Pearl:** Human chorionic gonadotropin (hCG) is a crucial tool in detecting and monitoring choriocarcinoma, a type of gestational trophoblastic disease. Elevated hCG levels can help in diagnosing, monitoring response to treatment, and predicting relapse in choriocarcinoma patients. It is essential for healthcare professionals to understand the appropriate markers for different tumour types to provide accurate diagnostic and therapeutic guidance to patients.