The adenoma-carcinoma sequence.

Evidence has been presented to show that most carcinomas of the large bowel develop in an adenoma, and that the life history of this sequence, although variable, probably takes on average 10 to 15 years. However, when the absolute numbers of adenomas and carcinomas are compared, it is apparent that the transition is uncommon. On a statistical analysis the malignant potential of adenomas is related to their size, growth pattern, and degree of epithelial atypia.

If the adenoma-carcinoma sequence is the norm, then a study of these criteria in adenomas at different sites in the colon and rectum would resolve the disparity in published series between the distribution of adenomas and carcinomas.