Gain of TP53 Mutation in Imatinib-treated SDH-Deficient Gastrointestinal Stromal Tumor and Clinical Utilization of Targeted Next-generation Sequencing Panel for Therapeutic Decision Support.

Patients with succinate dehydrogenase (SDH)-deficient gastrointestinal stromal tumor (GIST) have few therapeutic options. Despite lack of KIT or platelet-derived growth factor receptor A (PDGFRA) driver mutations, SDH-deficient GISTs display strong expression of KIT by immunohistochemistry and these patients are often treated with tyrosine kinase inhibitors, including imatinib as a first-line therapy. Using a targeted next-generation sequencing panel of mutation hotspots of 50-clinically relevant genes, we investigated (1) concurrence of somatic/actionable mutations and (2) tumor molecular evolution by comparing 2 resection specimens 1.5 years apart while the patient was on imatinib adjuvant therapy. We found the tumors did not harbor KIT, PDGFRA, or any other clinically actionable mutations. However, a TP53 mutation (c.422G>A; p.C141Y) was detected in the second recurrent lesion. This represents the first study to monitor the molecular evolution of a SDH-deficient GIST during adjuvant treatment. These findings emphasize the critical need for next-generation sequencing testing before initiating targeted therapy.