Robotic Duodenal Sleeve Resection for Gastrointestinal Stromal Tumor with Rare Exon 8 KIT Mutation Following Neoadjuvant Imatinib.

Gastrointestinal stromal tumors (GISTs) predominantly arise in gastric tissue, with only 5% occurring in the duodenum. While surgery remains the cornerstone of treatment, patients with large tumors or a high risk of recurrence may benefit from targeted therapy. Most GISTs harbor mutations in the KIT receptor tyrosine kinase, making them potentially responsive to tyrosine kinase inhibitors (TKIs) such as imatinib. Mutations in exons 9, 11, 13, and 17 are most common and are therefore included in most genetic panels. However, up to 15% of patients lack mutations in these exons and demonstrate variable responses to TKIs. This video demonstrates the management of a duodenal GIST located near the ampulla. Given the tumor's size and location, pancreaticoduodenectomy (PD) would likely be required for resection. Genetic testing was performed to assess the potential for targeted therapy to reduce tumor burden and allow for a more limited resection. Although no mutations were identified in exons 9, 11, 13, or 17, additional testing revealed a rare exon 8 KIT mutation. Exon 8 mutations have been reported in hematopoietic malignancies but are rarely described in GISTs, and their sensitivity to TKIs remains unclear. After informed consent, imatinib was initiated, resulting in a 30% reduction in tumor size at 6 months. The patient subsequently underwent a robotic duodenal sleeve resection with lateral duodenojejunostomy. His postoperative course was uncomplicated, and he was discharged on postoperative day 5. The patient received adjuvant imatinib and remains recurrence-free at three years. Given the rarity of exon 8 KIT mutations in GISTs, this mutation is not included in standard genetic panels. Although further study is needed, this case suggests that exon 8-mutant GISTs may respond to TKIs, potentially enabling less extensive surgical resection.