There are several precursor lesions seen prior to the development of colorectal adenocarcinoma.
Aberrant Crypt Foci / Hyperplasia / Dysplasia
The first abnormality, which is somewhat difficult to visualise macroscopically, is hyperplasia and dysplasia.
- Hyperplasia involves an increase in the number of cells and crowding, and is associated with ras proto-oncogene mutation
- Dysplasia involves dysplastic change within the epithelium and is associated with loss of APC.
Early adenomas are elevated (peduncular/sessile), flat or depressed
- Tubular adenomas, which contain flat, dysplastic mucosa and may be elevated or flat.
- Villous adenomas, with a leaf-like surface of small projections and are usually elevated