Abstract
Pathological characteristics of colorectal cancers and adenomas developing in 140 members of 34 Hereditary Non Polyposis Colorectal Cancer (HNPCC) families are described. In addition the pathological features of six cancers and 47 adenomas obtained from 216 at risk subjects in colonoscopic surveillance programmes are given. Survival rates for Dukes A,B and C cancers were 90%, 76% and 50% respectively, but only 32% of cancers were Dukes C. This would support the view that HNPCC malignancies are relatively non-aggressive, despite there being an excess of poorly differentiated and mucinous tumours. There is circumstantial evidence that evolution of malignancy occurs through the adenoma - carcinoma sequence.