Concurrent Coprimary KIT Exon 17 and BRAF Mutations in a Small Intestinal GI Stromal Tumor—A Case Report

Purpose: Gastrointestinal stromal tumors (GISTs) are rare neoplasms driven by mutations in KIT, PDGFRA, or BRAF. Concomitant KIT/BRAF mutations are exceptionally rare and have historically been regarded as mutually exclusive. We report the first documented instance of a GIST with concurrent KIT exon 17 (D816H) and BRAF exon 15 (V600E) mutations, exploring the implications of these mutations for treatment and prognosis. KIT exon 17 mutations are rare and associated with imatinib resistance, and the literature on concurrent KIT/PDGFRA and BRAF mutations is limited, highlighting the potential of this case to provide valuable insights into the management of similar tumors. Methods: A 70-year-old woman presented with abdominal pain and a 20-year history of intermittent melena. Imaging and histopathological examination confirmed a duodenal GIST. The patient underwent en bloc tumor resection, and next-generation sequencing (NGS) identified co-occurring KIT exon 17 (D816H) and BRAF exon 15 (V600E) mutations. Postoperatively, the patient received adjuvant imatinib therapy for a planned duration of 3 years. Results: The patient tolerated adjuvant imatinib therapy well, experiencing only mild nausea and diarrhea. After 2 years of follow-up, no recurrence of the tumor was detected, and the patient remained in radiological remission with no signs of metastasis or tumor progression. Conclusion: This case demonstrates a favorable outcome in a patient with localized GIST with concomitant KIT exon 17 and BRAF mutations following surgical resection with no evidence of recurrence. These findings underscore the significance of early comprehensive genotyping in GISTs to guide therapy and predict imatinib resistance.