Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the GIT. The majority harbor activating mutations in which gene?

• A PDGFRA exon 18
• B KIT (c-KIT) exon 11 ✓
• C BRAF V600E
• D NF1 (neurofibromatosis type 1 loss-of-function)

Explanation

Approximately 80–85% of GISTs harbor activating mutations in KIT (c-KIT), the majority in exon 11 (juxtamembrane domain), followed by exon 9 (extracellular domain). PDGFRA mutations (5–8%, mostly exon 18 D842V) are the second most common and are typically KIT-negative and imatinib-resistant (D842V). BRAF mutations are rare (<1%). NF1-associated GISTs are wild-type for KIT/PDGFRA and characteristically multifocal in the small intestine. Mutation type guides imatinib dosing: exon 11 responds to 400 mg/day; exon 9 requires 800 mg/day.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.