Background: Current American Cancer Society recommendations are that persons aged 50 years or older undergo screening flexible sigmoidoscopy every 3 to 5 years. In clinical practice, persons with adenomas at sigmoidoscopy are generally referred for full colonoscopy. However, cancers proximal to the splenic flexure may not be accompanied by neoplasia distal to the splenic flexure.
Methods: In order to estimate how often screening flexible sigmoidoscopy would be negative in persons with proximal cancer, we retrospectively reviewed 2053 consecutive colorectal cancer cases diagnosed from 1988 to 1994. Seven hundred ninety-nine (38.9%) had tumors proximal to the splenic flexure. We selected 358 study cases based on full colonoscopy performed and the colonoscopy reports available.
Results: Colonoscopy demonstrated distal adenomas in 77 cases (21.5%): 29 (8.1%) had hyperplastic polyps only, 4 (1.1%) had synchronous cancer, and 248 (69.3%) had no distal polyps. In this population, 77.4% of patients with proximal colon cancer had no distal neoplasia. We estimate that 30% of all patients with colorectal cancer would have a negative screening flexible sigmoidoscopy.
Conclusions: Prospective evaluation of colonoscopic findings in persons with proximal cancers is needed. Ongoing evaluation of colonoscopy as a general screening test is appropriate.