Colorectal de novo carcinoma: a review of its diagnosis, histopathology, molecular biology, and clinical relevance.

The effort to reduce colorectal adenocarcinoma mortality increasingly depends on detection and removal of precancerous adenomas by colonoscopy. Sporadic reports have described small, aggressive carcinomas that do not appear to develop from adenomas and have been called "de novo" carcinomas. These lesions seem to challenge the basis of colorectal surveillance and are therefore a controversial topic. This review presents the history of the de novo concept, the problems concerned with the histopathologic diagnosis of these lesions and what is presently known about their clinical and molecular biologic features in comparison with the more common ex adenoma type of colorectal carcinomas. This information will show that, despite their rarity, it is important for both pathologists and gastroenterologists to be aware of these lesions.