A sessile colonic polyp showing striking morphological changes within a 2-month period

Abstract

A 67-year-old man underwent total colonoscopy because he had had a positive fecal occult blood test. Colonoscopy showed a sessile polyp, 10 mm in diameter, in the sigmoid colon ([Fig. 1]). Six weeks later, he was scheduled for hospitalization to undergo endoscopic resection of this polyp. At this second colonoscopy the polyp was seen to have developed a morphologically unique “polyp on polyp” appearance ([Fig. 2]). Because invasive cancer was suspected on the basis of the endoscopic appearances, the endoscopic removal was discontinued and surgical resection was recommended. Nine weeks after the initial colonoscopy the patient underwent a third colonoscopy for endoscopic tattooing before surgery. Surprisingly, the polyp had transformed into a nonpolypoid lesion with a type V pit pattern ([Fig. 3]). Laparoscopy-assisted colectomy was performed, and on histological examination the resected specimen revealed a moderately differentiated adenocarcinoma without an adenomatous component, that extended deeply into the submucosal layer with vessel invasion and lymph node metastasis ([Fig. 4]).