Case 1, histopathological findings. (a) Resected specimen obtained by endoscopic ESD (H&E, ×4). (b) Foci of tubular adenoma with mild dysplasia (between the arrows) in the setting of HP (between arrowheads) are noted (H&E, ×20). (c) Foci of carcinomatous transformation (between red arrows) adjacent to the adenomatous lesion (black arrows) in sequence are observed (H&E, ×20). (d) The black box in (c) depicts the position of the enlarged section. Red arrows: foci of carcinomatous transformation; black arrows: adenomatous lesion. ESD: endoscopic submucosal dissection; HP: hyperplastic polyp.