Effectiveness of chemoradiation therapy with S-1 for patient 1 evaluated by colonoscopy and computed tomography. Colonoscopy was showing an ulcerative lesion in the lower rectum (A). Lymph node metastasis in the mesorectum was suspected using computed tomography (C). After chemoradiation therapy with S-1, colonoscopy showed a polypoid lesion (B). Biopsies revealed that there were no tumor cells, and lymph node metastasis had disappeared (D).