Folpe, Andrew

179 Background: GISTs arise from interstitial cells of Cajal anywhere within the gastrointestinal tract, but those of the esophagus and GEJ are exceedingly rare ( < 1% of cases). Our aim was to characterize clinicopathological features and outcomes of esophageal and GEJ GISTs and compare survival with a population-based registry (SEER). Methods: 28 cases were identified using the Mayo Clinic Cancer Registry from 1997 to 2016, and 378 cases from the SEER 18 registry from 2000 to 2013. Mayo cases were re-reviewed by Mayo pathologists. We analyzed patient characteristics, tumor location, TNM staging, mitotic index, molecular diagnostics, IHC staining, and histomorphology. JMP software was used to calculate time to recurrence (TTR) and overall survival (OS) utilizing Kaplan-Meier and log-rank. Results: At Mayo, 60% of tumors arose in the distal esophagus. Mean tumor size was 5.73 cm. 42% of cases were low grade. None had nodal involvement. Five cases were metastatic at diagnosis, all to the liver. 86.7% had spindle cell morphology. IHC staining was positive for KIT in 92%, followed by CD34 (52%), DOG-1 (24%), and actin (16%). Mutational analysis was done on 10 cases and KIT mutation was found in 8 cases; 2 were wild-type. Two-thirds of patients underwent surgery, mostly esophagectomy. 14 patients received adjuvant imatinib. Median time to diagnosis from symptom onset was 2 months; median time to surgery from diagnosis was 1 month. Of 10 patients with complete follow-up, 2 had recurrences: 1at the anastomotic site and 1 in the liver. Median TTR from surgery was 36.5 months. Median follow-up time was 31.5 months. Median OS from diagnosis for the Mayo cohort was 129.5 months (95% CI 55.7-x). SEER cohort median OS was 81 months (95% CI 63-101), and females had superior OS compared to males (HR 0.67; 95% CI 0.48-0.93, p = 0.016). Conclusions: Patients undergoing surgical resection for esophageal and GEJ GISTs had a favorable prognosis, but recurrences occurred. The superior OS seen in the Mayo cohort suggests early resection and adjuvant imatinib may improve outcomes.