CLINICAL INVESTIGATION OF COLORECTAL-CANCER DETECTED BY FOLLOW-UP COLONOSCOPY AFTER ENDOSCOPIC POLYPECTOMY

PURPOSE We analyzed the results of a long-term follow-up surveillance of patients with colorectal polyps after endoscopic polypectomy in ter ms of the cumulative incidence of subsequent colorectal cancer and the clinicopathologic characteristics of carcinomas detected by colonosco py. METHOD: The study cohort consisted of 6,715 patients who had recei ved endoscopic resection of single or multiple colorectal polyps and t hen underwent periodic colonoscopy (or a combination of sigmoidoscopy and barium x-ray examination in some cases) during an average follow-u p of six years (40,622 person-years in total). RESULTS: During the fol low-up, 31 cases of colorectal cancer containing 15 submucosal invasiv e carcinomas (T1,N0,M0) and 16 advanced carcinomas were detected. The cumulative incidence of colorectal cancer was analyzed for four subgro ups of the 6,715 patients classified according to the diameter, grade of dysplasia, and histologic features of polyps. Furthermore, the dept h of invasion, macroscopic configuration of submucosal invasive cancer , and site of colorectal cancer observed in the 31 cases were compared with those of a reference group of 1,497 patients with colorectal can cer treated at Takano Hospital during the same period. Submucosal inva sive cancer was the most common type among the colorectal carcinomas d etected during follow-up. In terms of macroscopic configuration of sub mucosal cancer, the superficial type was significantly more common tha n the protruded type. The superficial submucosal cancer showed a signi ficantly longer interval to detection than the protruded submucosal ca ncer. By site of lesion, proximal colon cancer was significantly more common. CONCLUSION: Followup colonoscopy appears to be useful in patie nts with larger polyps (>5 mm). Patients with severe dysplasia and tho se with malignant polyps should be followed-up carefully. Because subm ucosal cancer detected by follow-up examination after polypectomy show ed higher rates of superficial-type cancer and proximal colon cancer, careful endoscopic examination of the entire colon is important.