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Which Colonic Adenomas Became Malignant?

TO THE EDITOR: The study by Koretz [1] is controversial and the conclusions are based on historical data and the premise that colonic adenomas represent a homogeneous group. Rather, one can divide colonic adenomas into two groups: those that do not become malignant (uncommitted to malignant transformation [>95% of all sporadic colonic adenomas]) and those that transform into adenocarcinomas (committed to malignant transformation [<5% of all sporadic colonic adenomas]). Evidence suggests that several histologic subtypes differ in risk for malignant transformation. Analyses of so-called flat adenomas [2] and serrated adenomas [3] suggest that these lesions transform into carcinoma (not degenerate into carcinomas as Koretz states) more frequently than ordinary colonic adenomas and do so when relatively small. It is not known if all colonic adenomas have the same growth rate or growth potential, or if flat and serrated adenomas require less time to become malignant than ordinary adenomas. In short, Koretz is analyzing several different adenoma subgroups that have not been adequately characterized. More importantly, it is difficult to study a small subpopulation using data obtained from entire populations at risk. Analyses of malignant polyps resected through colonoscopy indicate that up to 15% of these will be 1.0 cm or less in diameter [4, 5]. This indicates that the data available from the analysis of all the existing colonic adenomas cannot successfully be used to study the subpopulation of committed adenomas. To draw a parallel: Little information would be gained about lung carcinomas by analyzing multiple variables in the entire U.S. population. More meaningful information becomes available by studying only the affected group.