Flat adenomas exist in asymptomatic people: important implications for colorectal cancer screening programmes

Abstract

Background-Flat adenomas are nonexophytic with a flat top or central depression and histologically the depth of dysplastic tissue is never more than twice the mucosal thickness. Flat adenomas frequently contain severely dysplastic tissue, and may progress rapidly through the adenoma-carcinoma sequence. Flat lesions have never been described in a British asymptomatic population. Aims-To determine whether flat adenomas exist in an asymptomatic population participating in a large randomised controlled trial of flexible sigmoidoscopy screening. Patients-A total of 3000 subjects (aged 55-64 years) underwent screening by flexible sigmoidoscopy. Methods-All polyps were removed and sent for histology. The number of polyps with endoscopic and histological features of flat adenomas was recorded. Results-Three subjects had a total of four flat lesions-that is, one per 1000 people screened. Three contained severely dysplastic tissue, one a focus of adenocarcinoma. Three of the four lesions were less than 5 mm in size and the fourth was 15 mm in diameter. Conclusions-Flat lesions with severe dysplasia exist in the asymptomatic population. This has major implications for gastroenterologists who should be trained to identify them. Their existence is of importance to molecular biologists and epidemiologists investigating the aetiology of colorectal cancer. (Gut 1998;43:229-231)

Hereditary nonpolyposis colorectal cancer

“…The converse appears to apply in the case of sporadic adenomas. In flat adenomas, which are known to be relatively aggressive, K-ras mutations may not occur at all [39].…”

Pathological features and genetic alterations in colorectal carcinomas with characteristics of nonpolypoid growth

“…It is likely that the biologic behaviour of NPG carcinomas is more aggressive than that of PG carcinomas. Many reports have analysed that flat and depressed lesions have a higher malignant potential than polypoid lesions, since flat and depressed lesions readily infiltrate deeper layers despite their small size (Crowford and Stromeyer, 1983;Wolber and Owen, 1991;Lanspa et al, 1992;Jaramillo et al, 1994;Rubio et al, 1994;Kudo et al, 1995a, b;Mitooka et al, 1995;Yokota et al, 1995;Fujii et al, 1998;Hart et al, 1998;Rembacken et al, 2000;Saito et al, 2001). A greater malignant potential in NPG carcinomas than in PG carcinomas is analogous to flat lesions containing depressed areas having greater malignant potential than polypoid adenomas.…”

Role of colonoscopy in colorectal cancer

“…Histologically, they are tubular adenomas where the height of the adenomatous component does not exceed twice the height of the surrounding normal mucosa. A high incidence of atypia has been consistently reported for flat adenomas 26 , and there is a general assumption not only in Japan 27,28,29,30 that CRC can rapidly arise from these diminutive lesions, which can be missed in conventional colonoscopy.…”