Question

Which of the following markers is specific for gastrointestinal stromal tumors (GIST)?

• A. CD117
• B. CD34
• C. CD23
• D. S-100

Hint:

Think c-KIT receptor and the drug imatinib.

Answer 1

The Correct Option is A

Step 1: GIST arises from the interstitial cells of Cajal, the pacemaker cells of the gut wall. Most cases carry an activating mutation in the c-KIT gene.
Step 2: The c-KIT gene codes for a tyrosine kinase receptor whose protein is detected by the antibody CD117. Because nearly all GISTs overexpress this receptor, CD117 positivity is the defining and most specific marker of the tumour.
Step 3: This marker is also clinically important because CD117 positive tumours respond to imatinib, a tyrosine kinase inhibitor.
Step 4: Why the others are wrong. CD34 is positive in many GISTs but it is not specific, since it also marks vascular and other mesenchymal tumours. CD23 is a marker of follicular dendritic cells and small lymphocytic lymphoma/CLL. S-100 marks nerve sheath tumours and melanoma. None of these is specific for GIST.
Step 5: Therefore the specific marker is CD117.
Answer: Option A (CD117).