Fig. 1

Preoperative colonoscopy. A Initial colonoscopy shows a rectal tumor below the peritoneal reflection 5 cm from the anal verge, occupying three quarters of the circumference. B Colonoscopy after chemoradiation therapy shows that the tumor responded clinically, and there is no evidence of the previous features, except for a flat white scar and telangiectasias. At the distal end of the tumor, the mucosa is reddish and swollen. Hematoxylin and eosin-stained sections (C, × 20. D, × 100.) show a well-differentiated adenocarcinoma with a partially tubular structure