Background: The risk of invasive carcinoma developing in colorectal adenomas is influenced by a number of characteristics of both patients and adenomas, and the composition of the sample analysed.
Patients and methods: Between 1978 and 1993 more than 20,000 polyps were prospectively documented at the Erlangen Registry of Colorectal Polyps, and analysed statistically by logistic regression.
Results: The size of the adenomas proved to be the most important factor for adenomas equal to or larger than 15 mm as compared with smaller lesions. In 5,137 diminutive adenomas (< or = 5 mm) invasive carcinoma was never found. Adenomas in the right-sided colon had a lower risk than those in the left colon or rectum, but with increasing adenoma size, the malignancy rate showed a right-sided shift. In adenomas of up to 36 mm in diameter, invasive carcinoma was found more often when they were located in the rectum or left colon while adenomas larger than 36 mm were more likely to harbour invasive carcinoma when located in the right or left colon rather than in the rectum.
Conclusions: A multivariate analysis of 11,380 adenomas detected at the first total colonoscopy showed that the factors size and site, both of which can be assessed by endoscopic inspection alone, were found to enable a statistically and clinically adequate assessment of the malignancy risk.