Incidence and treatment outcomes of metachronous gastric cancer occurring after curative endoscopic submucosal dissection of undifferentiated-type early gastric cancer: Japan Clinical Oncology Group study—post hoc analysis of JCOG1009/1010

Background and aims A drawback of endoscopic submucosal dissection (ESD) for early gastric cancer (EGC) is the development of metachronous gastric cancer (MGC). While MGC after ESD for differentiated-type (D-) EGC was well understood, little is known about MGC occurring after ESD for undifferentiated-type (UD-) EGC, because ESD had not been indicated. We evaluated the incidence and treatment outcomes of MGC after ESD of UD-EGC. Methods This study is a post hoc analysis of JCOG1009/1010, a multicenter trial to evaluate the efficacy and safety of ESD for UD-EGC. The patients who underwent curative ESD of index solitary UD-EGC were analyzed. Surveillance endoscopy was performed biannually for the first 3 years and thereafter annually. We assessed the time to MGC occurrence after ESD, lesion characteristics, and treatment outcomes of MGC. Time to MGC occurrence was estimated by cumulative incidence function, with death and total gastrectomy as competing risks. Results A total of 198 patients were included in this study. During a median follow-up period of 5.8 years, 4 patients (2%) developed MGC. Median time to MGC occurrence was 4.5 years (range: 3.1–5.4). Five-year cumulative incidence of MGC was 1.0% (95% CI: 0.2–3.3%). Two MGCs were histologically D-EGC, and the remaining two were UD-EGC. The median tumor size of MGCs was 1.0 cm (range: 0.7–1.7), and the depth of invasion (M/SM1/SM2) was 2/1/1, respectively. Three patients achieved curative resection with repeated ESD. Conclusions MGC does not occur commonly after curative ESD of UD-EGC, and repeated ESD could contribute to stomach preservation.