ArticlesFlat and depressed colonic neoplasms: a prospective study of 1000 colonoscopies in the UK
Introduction
The adenoma-carcinoma hypothesis proposes that colorectal cancers arise from adenomatous polyps.1 Morson2 estimated that up to two-thirds of all colorectal carcinomas arise from adenomatous polyps, but was unable to explain the origin of the remainder. Japanese workers have reported the existence of flat and depressed tumours since the 1980's.3, 4, 5 Retrospective reviews indicate that 12–40% of adenomas or early colorectal carcinomas appear flat, or as depressions, rather than polyps.6 Outside Japan however, there have been few reports of such lesions.7, 8, 9 Although there is a higher incidence of colonic cancer in Europe and the USA than in Japan, flat or depressed lesions have been regarded as rare in western countries. Lanspa et al,10 suggested that flat adenomas might have the same prevalence as other adenomas in the USA, and that they may represent an early stage of adenoma formation. Fujii et al11 reported that up to two-thirds of adenomas in a small prospective study of 210 patients in the UK, appeared flat or depressed.
The polyp-carcinoma hypothesis has led to the hope that screening to clear the colon of polyps would reduce the risk of colorectal cancer.12 If flat and depressed tumours are commoner than previously thought, it would have important implications for cancer prevention programmes because these lesions are more difficult to detect. We have therefore undertaken a large prospective study to determine the prevalence and distribution of flat or depressed neoplasms in the UK.
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Methods
1000 consecutive, unselected patients attending for routine colonoscopy in Leeds and Bradford were screened for flat or depressed neoplasms by a single colonoscopist (BJR). Informed consent was obtained from all patients. Mean age was 59 years (range 15–98) with a male/female ratio of 7/10.
All colonoscopies were done between June 1995 and March 1999, with a standard Olympus 200L colonoscope and the 200Z magnifying colonoscope. Bowel preparation included 2–5 L polyethylene glycol electrolyte
Results
We identified a total of 321 adenomas in 225 patients, six Duke's A carcinomas in six patients, and 25 more advanced carcinomas in 24 patients. 111 lesions were treated by hot biopsy, 89 pedunculated lesions were removed by snare polypectomy, and 82 flat lesions were removed by endoscopic resection. 66 lesions were sampled by biopsy and, excluding the advanced carcinomas, four lesions were removed at surgery. There were several features that suggested the presence of cancer within a lesion.
Discussion
Although up to two-thirds of colorectal carcinomas might develop from adenomatous polyps,2, 5 some workers have suggested that colorectal cancer can also develop de novo from normal mucosa.22 In support of this de novo theory, several series of early colonic carcinomas, without evidence of concomitant adenomatous tissue, have been published.23, 24, 25 In the largest series, 155 small carcinomas were identified without evidence of concomitant adenomatous tissue;24 59% of the lesions appeared
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