Metachronous multiple gastric cancer discovered as endoscopic curability C2 during regular follow-up after gastric ESD.

[Objectives] To clarify characteristics of metachronous endoscopic curability C2 cancer (eCura C2) during post-endoscopic submucosal dissection (ESD) follow-up. [Methods] Of 4355 gastric lesions treated by ESD at our hospital during 2005-2021, 657 were metachronous. After excluding lesions found 2 years since the prior examination or in the gastric remnant, the remaining 515 were analyzed. [Study 1] We compared 35 eCura C2 cancers and 480 eCura A-C1 cancers. [Study 2] Endoscopic findings of the 35 lesions were examined to determine why they had been missed. [Results] Mean tumor size was larger (34.0 mm vs. 12.1 mm, p0.01) and the proportions of mixed-type and poorly differentiated cancers were higher (highly:mixed:poorly, 34.3:57.1:8.6 vs. 94.2:5.0:0.8, p0.01) in the eCura C2 group. [Study 2] At the prior examination, 4 lesions were noticed but considered benign, 2 lacked sufficient imaging, 19 were detectable on imaging but missed, and 10 were not detectable on imaging. Over half the lesions that were detectable but missed at the prior examination were in the lesser curvature, many being type IIa-IIb lesions with color similar to the background mucosa. All lesions not detectable on imaging at the prior examination were mixed type or poorly differentiated type. [Discussion] Metachronous cancer detected as eCura C2 cancers was significantly larger, and a significantly higher proportion was mixed-type or poorly differentiated cancers, compared with eCura A-C1 cancers. Possible reasons why these lesions were missed include rapid progression of mixed-type and poorly differentiated cancers, and poor recognition that lesions showing only slight color changes may be present at the lesser curvature.