Fig. 2.

 Case 2. a Colonoscopy shows a reddish-elastic hard submucosal tumor. b Magnification endoscopy with narrow-band imaging revealed findings similar to the tree-like appearance of abnormal microvessels on the thin layer of mucosa. c Oral-side dissection was performed first with an ITknife nano with a retroflexed view. d We continued the dissection just above the muscle layer, and stopped the dissection at the point where the muscle layer was retracted toward the tumor. e Resected specimen showing a 30 mm tumor. f, g Pathological findings in the resected specimen showing diffuse atypical lymphocytes with centrocyte-like cells in the mucosa and submucosal layer. Immunohistochemical staining findings were compatible with a diagnosis of mucosa-associated lymphoid tissue (MALT) lymphoma with focal diffuse large-cell B-cell lymphoma (DLBCL) transformation.