Invasive carcinoma in colorectal adenomas: multivariate analysis of patient and adenoma characteristics

The risk of invasive carcinoma developing in colorectal adenomas is influenced by a number of characteristics, relating both to the patients and to the adenomas, and by the composition of the sample analyzed. The aim of the present study was use a multivariate analysis to investigate the risk of invasive carcinoma in endoscopically and surgically removed adenomas.

Between 1978 and 1993, more than 20,000 polyps were prospectively documented at the Erlangen Registry of Colorectal Polyps. A multivariate analysis of 11,188 adenomas detected at the first total colonoscopy was carried out in order to investigate the risks associated with size and site--both of which can be assessed by endoscopic inspection alone- and the extent to which these may be modified by other patient and adenoma characteristics, with an influence on the risk of invasive carcinoma in colorectal adenomas.

The size of the adenoma proved to be the most important influencing factor. Invasive carcinoma was never found in 5027 small adenomas (< or = 5 mm). Adenomas in the right 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, with a significant interactive effect of size and right-sided location. However, the risk determined by the size and site of the adenoma was significantly modified by a number of patient and adenoma characteristics, including histological type, presence of multiple adenomas, and patient age and sex.

The risk of invasive carcinoma in colorectal adenomas can only be adequately described by a complex model of the interactive effects of patient and adenoma characteristics on the main factors of size and site.