A 64-year-old woman complains of intermittent abdominal discomfo in the right iliac fossa along with loss of appetite and significant weight loss over 6 months. She was managed conservatively. She presented 2 days later with a cramping abdominal pain at the same location along with diarrhoea. During these episodes her husband has commented that she looked red in the face. CECT abdomen was done. Which of the following tumour markers can be seen raised in the above condition: –

**Core Concept**
The patient's symptoms and presentation are suggestive of a gastrointestinal malignancy, specifically carcinoid tumor, which is a type of neuroendocrine tumor. Carcinoid tumors can cause flushing, diarrhea, and abdominal pain due to the release of serotonin and other vasoactive peptides.

**Why the Correct Answer is Right**
The correct answer is related to the tumor marker 5-Hydroxyindoleacetic acid (5-HIAA). Carcinoid tumors produce serotonin, which is metabolized to 5-HIAA. Elevated levels of 5-HIAA in the urine are a hallmark of carcinoid syndrome, which is characterized by flushing, diarrhea, wheezing, and abdominal pain. The patient's symptoms, particularly the flushing and diarrhea, are suggestive of carcinoid syndrome. The measurement of 5-HIAA in the urine is a specific test for diagnosing carcinoid syndrome and can help confirm the diagnosis of a carcinoid tumor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CEA (Carcinoembryonic antigen) is a tumor marker that is elevated in various types of cancer, including colorectal, lung, breast, and pancreatic cancer, but it is not specific for carcinoid tumors.
**Option B:** This option is incorrect because CA 19-9 is a tumor marker that is elevated in pancreatic cancer, but it is not specific for carcinoid tumors.
**Option C:** This option is incorrect because CA 125 is a tumor marker that is elevated in ovarian cancer, but it is not specific for carcinoid tumors.

**Clinical Pearl / High-Yield Fact**
Carcinoid tumors can be challenging to diagnose, and the measurement of 5-HIAA in the urine is a key diagnostic test. It's essential to consider carcinoid syndrome in patients with unexplained flushing, diarrhea, and abdominal pain, especially if they have a history of gastrointestinal symptoms.

**Correct Answer:**
Correct Answer: A. 5-Hydroxyindoleacetic acid (5-HIAA).

✓ Correct Answer: A. Synaptophysin