P-OGC67 Gastric GISTs: Can presentation, Location and Radiological Features predict behaviour? – Experience in a UK cohort

Abstract

Abstract Background Gastrointestinal stromal tumours (GISTs) most commonly arise in the stomach, vary significantly in behaviour and can be difficult to risk stratify accurately pre-operatively. They are increasingly being identified incidentally during endoscopies or cross-sectional imaging. They have malignant potential and but vary from very low to high-risk. Pre-operatively, histological diagnosis can be achieved by performing endoscopic ultrasound (EUS) guided fine-needle aspirate or biopsy, but samples often contain insufficient material. This study aims to assess other features help identify aggressiveness of GISTs pre-operatively to help guide management decisions. Methods This is a retrospective cohort study analysing patients treated surgically for GIST from 2011-2020 at a UK tertiary centre. Exclusion criteria were non-gastric GISTs and patients who received a different diagnosis post-operatively. Hospital electronic patient record and e-noting systems were used to collect data. Risk groups were stratified according to the NCCN risk classification for GIST. ‘Very low risk’ and ‘low risk’ groups were combined in the analysis to form the ‘lower risk’ group; ‘moderate risk’ and ‘high risk’ categories combined to form the ‘higher risk’ group. Statistical analyses were conducted using STATA version 15. Results 171 patients were included in total. OGD diagnosed gist on histology if ulcerated in 14.7% of cases. EUS biopsy was performed in 39% of cases pre-operatively – 84.6% of these were diagnostic. There was a higher proportion of higher risk GISTs in the GOJ/cardia region than lower risk GISTs (16.2% versus 6.7%), though this did not reach statistically significance (p = 0.32). A greater proportion of higher risk tumours were irregular in outline (p=.26), heterogenous (p = 0.003) and necrotic (p = 0.001) than lower risk tumours. In addition, higher risk tumours were significantly more likely to be exophytic than lower risk tumours, which were significantly more endophytic (p = 0.05). A ROC curve including all the variables had an AUC of 0.8971. Conclusions This is the largest analysis of gastric GISTs in a UK population. This study found that a higher proportion of higher risk tumours were irregular, heterogenous and necrotic than lower risk tumours. In this study, a greater proportion of higher risk tumours arose in the GOJ/cardia. In keeping with muscularis origin, endoscopic biopsy was found to be a poor diagnostic tool unless ulcerated. EUS and FNA biopsies had a much higher rate of histological confirmation. This knowledge might help facilitate a more individualised approach with non-operative surveillance in lower risk tumours or expedited surgery in higher risk lesions.