Adenomatous lesions of the large bowel: an autopsy survey.

A comprehensive autopsy survey of the large bowel showed that adenomas were very common lesions occurring in about one-half of the 518 cases studied. The great majority were small adenomatous polyps (tubular adenomas), 86.7% measuring less than 10 mm in diameter. Adenomas with a more complex tubulovillous pattern were larger with a mean diameter of 19.0 mm. There was no apparent incresae in mean size of adenomas with age. Nineteen clinically unsuspected cancers were discovered. Fourteen (8 in situ and 6 invasive) cancers had areas of residual benign adenoma. Five invasive cancers had no residual benign component. No in situ carcinomas or small (less than 10 mm) invasive cancers not containing residual adenoma were found. The results suggest that, although adenomas of the large bowel are very common, the vast majority are simple adenomatous polyps which do not undergo progressive growth and malignant change. Conversely, it appears that cancers may arise from benign adenomas which have the characteristics of large size and a more complex villous architecture.