Distribution of colorectal cancers and adenomas in a screened population and the effectiveness of flexible sigmoidoscopy as a lone screening tool

DAL Macafee, MRCS ^a, JH Scholefield FRCS^a, DK Whynes BA, BP ^b

^aDivision of GI Surgery, Queens Medical Centre, Nottingham, United Kingdom, ^bDepartment of Economics, University of Nottingham, Nottingham, United Kingdom

Aim: A “proximal shift” in the site distribution of colorectal cancer (CRC) has been reported in symptomatic populations. Firstly, the study investigated whether such a shift in tumour site was evident within the test group of a screened population. Secondly, the distribution of adenomatous polyps was evaluated. These findings were subsequently used to assess the effectiveness of flexible sigmoidoscopy as a lone screening tool. Methods: Between February 1981, and January 1991, 152 850 people aged 50 -74 years, were recruited to a randomised controlled faecal occult blood testing (FOBT) screening study (Nottingham,UK). Only those allocated to FOBT screening (76 466) were included in this analysis. The site of cancer or adenoma was determined from operation notes and pathology reports. Examination of the left colon, was defined as viewing the rectum, sigmoid and descending colon. Flexible sigmoidoscopy was considered to reach the splenic flexure or the recto-sigmoid junction in two separate analyses. Results: Cancers: 36.6% (576) of cancers were noted in the rectum, 27.9% (432) in the sigmoid colon and 17.7% (274) in the caecum. Adenomatous polyps: 35.0% (522) of adenomas were noted in the rectum, 51.1% (761) in the sigmoid colon and 2.7% (40) in the caecum. Flexible sigmoidoscopy (FS): 68.3% (1060) of cancers and 91.8% (832) of the adenomas present would have been directly visualised by FS to the splenic flexure. Conclusions: The distribution of colorectal cancers and adenomas in the test group of a screened population appear similar to those in general populations. The results suggest that there may be a trend towards an increasing prevalence of right-sided cancers and this could have significant implications when choosing an effective screening tool. Whether this is a true shift or a reduction in the incidence of rectal and left-sided cancers, remains unclear. Adenoma distribution remains predominantly left-sided with over 90% potentially within reach of flexible sigmoidoscopy.

Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in oral session 992 (Screening & detection - Part I).