A 50-yr-old male presents with obstructive symptoms. Biopsy of stomach reveals Gastrointestinal stromal tumor (GIST). Most appropriate marker for GIST is:
**Core Concept**
The underlying principle being tested is the identification of a specific tumor marker for **Gastrointestinal stromal tumors (GISTs)**, which are the most common mesenchymal neoplasms of the gastrointestinal tract. GISTs are known for their association with **tyrosine kinase receptors**.
**Why the Correct Answer is Right**
The most appropriate marker for GIST is **CD117 (c-KIT)**, a tyrosine kinase receptor. GISTs often express **CD117**, which is a key diagnostic marker. The expression of **CD117** is due to mutations in the **c-KIT** gene, leading to the activation of tyrosine kinase activity.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not specifically associated with GIST.
**Option B:** Incorrect as it is more commonly associated with other types of tumors.
**Option D:** Incorrect because, although it can be positive in some cases, it is not the most specific marker for GIST.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **CD117 (c-KIT)** positivity is crucial for the diagnosis of GIST and also has implications for treatment, as **tyrosine kinase inhibitors** like imatinib are effective in treating GISTs.
**Correct Answer:** D. CD117