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Objective-To introduce and monitor a screening programme for first degree relatives of patients with colorectal cancer based on their calculated lifetime risk.Design-Lifetime risks were calculated for first degree relatives of patients with colorectal cancer and used to offer screening based on estimated risk.Setting-A family cancer clinic was set up as part of the North East Thames Regional Genetic Service for relatives ofpatients who had developed colorectal cancer before the age of 45 and members of families in which multiple cancer had occurred.Patients-Self referrals as well as patients referred by general and hospital practitioners.Intervention-Relatives with a lifetime risk of 1 in 10 or greater (high risk group) were offered screening five yearly by colonoscopy, and those whose risk was between 1 in 10 and 1 in 17 were offered yearly screening for faecal occult blood. Women with family histories compatible with Lynch type II cancer family syndrome were offered screening for breast and pelvic tumours.Results-In four years 715 patients were seen. Acceptance of screening was 90% (644 patients). Of 151 patients screened for faecal occult blood, two were found to have polyps. This screening test was unsatisfactory for the high risk group, having a negative predictive value of 78% in 59 patients tested. Regular screening by colonoscopy was offered to 382 high risk patients; 62 patients with polyps and five with colonic cancer were found. One hundred and ten pedigrees were identified with the Lynch type II cancer family syndrome, and four of 35 women screened were found to have breast cancer. Of 14 relatives aged over 65 with a 1 in 2 risk of site specific colonic cancer or Lynch type II cancer family syndrome, seven were found to have polyps, one of whom had carcinoma in situ.Conclusions-Family history can be used to identify those at risk of colonic cancer and to target appropriate screening. Colonoscopy detected a high number of premalignant colonic polyps, but faecal occult blood testing was unsatisfactory for those at high risk of colorectal cancer. IntroductionThe lifetime risk of death from colorectal cancer in England and Wales is approximately 1 in 50 and increases rapidly from age 50. Unfortunately, the results of treatment are disappointing with an acknowledged survival rate of 50% in patients undergoing surgery with a view to cure. In 1974 Morson pointed

Examination of the entire sigmoid was not achieved in approximately one-quarter of patients undergoing screening flexible sigmoidoscopy, mainly because of discomfort. The descending colon is intubated in a minority of cases (using standard instruments), even after 60 cm has been inserted. Alternative instruments with different shaft characteristics (floppy, narrow calibre, 80-100 cm in length) may be necessary to ensure deeper routine intubation in nonsedated patients.

In the three years since fibreoptic colonoscopes became generally available there have been a number of reportsl-12 and reviewsl3-14 describing the clinical value of colonoscopy. The technical difficulties and time involved in the procedure, the initial expense of the instruments, and the need for x-ray facilities have discouraged many centres from becoming involved in colonoscopy. Colonoscopy and biopsy has, however, been shown to be more accurate in diagnosis than barium enema89, ,12 and to remove the need for laparotomy in many cases; colonoscopic polypectomy15,61617p18p1 is now a practicable alternative to abdominal operation. It has therefore become mandatory on economic as well as clinical grounds that colonoscopy should be generally available, but because some technical difficulties remain it is also important that its indications, limitations, and relationship to radiological methods are understood. Much of the literature on colonoscopy has to date been in obscure or specialized journals, individual experience has been small, and variations in technique have been considerable. This review is therefore augmented by personal contacts with colonoscopists throughout the world and by experience of over a thousand colonoscopies. Because of the technical problems involved practical aspects of the procedure are covered in some detail. Instruments An ACMI fibreoptic colonoscope was produced in 196320 but the first instruments with manoeuvrable tips appeared in Japan in 19667 and in Europe in 1969-1970 as the fibresigmoidoscopes of Olympus (CF-SB), Machida (FSS), and subsequently ACMI (Overholt 9000)-all now outdated. The current instruments have four-way tip angulation, air, water, and suction controls, and biopsy facilities but may be 'medium' (105-110 cm: Olympus CF-MB; Machida, FSM, ACMI 9000P) or 'long' colonoscopes (165-185 cm: Olympus CF-LB; ACMI 9000PL, Machida FCS). Fuller details are given elsewhere21. Of the commonly used colonoscopes the shorter instruments have proved easier to use, but limit the examination to the left colon. The ACMI instruments as a whole are more robust while those from Olympus have more convenient controls and sharper optics. A new generation of 'operating colonoscopes' is now being presented with either a single large channel, snare deflector, and CO2 control (Olympus CF-MB2, CF-LB) or two channels and integral stiffness control (ACMI F9A). Wolf, Saas-Wolf, and Storz endoscopes are not yet in general use A wide range of essential accessories is available including fibreoptic 'teaching aids', excellent spiked biopsy forceps (ACMI), cytology brushes (ACMI, Olympus), polypectomy snares (ACMI, Olympus, Storz), and the new stiffening tubes described later. Adaptors are available to interconnect ACMI instruments with Olympus light sources and cameras and it is hoped 990