Early malignant lesions of the colorectum at autopsy

Examination of 1014 consecutive autopsies revealed four early malignant lesions, comprising: 1) a carcinoma in situ arising from a large (2.5 cm) pedunculated adenomatous polyp; 2) a carcinoma in situ arising from a small (0.8 cm) flat adenoma; 3) an early invasive carcinoma arising from a flat (2.5 cm) adenoma, and 4) an early invasive polypoid adenocarcinoma (0.7 cm) with no identifiable remnants of adenoma. The early malignant lesions encountered in this study reaffirm the importance of the adenoma-cancer sequence in the pathogenesis of colorectal cancers in man. The malignant potential of flat adenomas is emphasized. The occurrence of small carcinomas without evidence of adenomatous elements raises the possibility of de novo origin as an alternative pathway. In the present study, one of four early colorectal cancers may have a de novo origin.