Diagnostic additional effect of EUS for gastric cancer suspected of submucosal invasion by conventional endoscopy; a multicenter prospective study

In the diagnosis of early gastric cancer (GC) invasion depth, we proposed previously an integrated strategy by conventional endoscopy (CE) and EUS, which may offer efficient and accurate diagnosis. However, it was a single-center retrospective study. We thus conducted a multicenter prospective study, from May 2017 to Jan 2021, to validate the diagnostic algorithm and to clarify the additional effect of EUS for submucosal (SM) invasive cancer. In each case, the diagnosis was made by CE, followed by EUS, and finally by combination. A total of 180 patients with diagnosed or suspected SM invasive GC by CE were enrolled at 11 institutions, and 172 cases were analyzed. Histopathological depth was M 71/SM1 16/SM2 63/MP or deeper 22. The treatment included 91 ESD cases and 81 surgery cases. Diagnostic accuracy classified by M-SM1 or SM2-MP was 58.1% for CE, 75.9% for EUS, and the accuracy rate for final combination algorithm diagnosis (79.1%) was significantly higher than that for CE alone. The additive effect of EUS was found in CE-SM low-confidence cases but not in CE-SM high-confidence cases. Irregular surface, SMT-like elevation, and non-extension sign were independently significant markers of SM. More than 95% could be resected endoscopically with negative vertical margins in EUS-M cases. In conclusion, EUS has an additional effect in CE-SM low-confidence cases.