Supplementary Material for: Clinical impact of proton pump inhibitor and potassium-competitive acid blocker for predicting the curability of endoscopic resection in ulcerative early gastric cancer

Background: Endoscopic diagnosis is essential for predicting the curability of early gastric cancer (EGC; R0 resection) before treatment, but the relationship between ulcerative lesions and clinical outcomes remains unclear. We aimed to investigate the effect of proton pump inhibitor (PPI) or potassium-competitive acid blocker (P-CAB) on the morphological changes of ulcerative EGCs and its relevance to the clinical outcomes. Methods: Altogether, 143 patients with differentiated ulcerative EGC that were resected by endoscopic submucosal dissection were retrospectively identified and divided into the following two cohorts depending on their PPI/P-CAB administration status: PPI/P-CAB (n = 76) and non-PPI/P-CAB (n = 67) cohorts. Furthermore, in each cohort, the patients were further divided into the improved and unimproved subgroups based on the ulcerative changes. Results: In the PPI/P-CAB cohort, the deep submucosal invasion and lymphovascular invasion rates were significantly higher in the unimproved subgroup than in the improved subgroup, resulting in a significantly lower R0 resection rate. Contrarily, no significant differences were found between the two subgroups in the non-PPI/P-CAB cohort. The significance of PPI/P-CAB administration was observed only in the ulcerative EGCs with open-type atrophy (R0 resection rate; improved vs. unimproved, 90.9% vs. 48.0%, p = 0.001). When the finding of improved ulcer with PPI/P-CAB administration was used as the indication of endoscopic resection in ulcerative EGCs with open-type atrophy, high sensitivity (78.9%) and accuracy (76.3%) rates for the curability were observed which were higher than those of conventional endoscopic diagnosis alone (p = 0.021). Conclusion: PPI or P-CAB administration might contribute to the potential selection of ulcerative EGCs, enabling endoscopic curative resection.