Identification of an intermediate signature that marks the initial phases of the colorectal adenoma-carcinoma transition.

The colorectal adenoma-carcinoma sequence describes the stepwise progression from normal to dysplastic epithelium and then to carcinoma. Only a small proportion of colorectal adenomas (CRAs) progress to colorectal carcinomas (CRCs). Endoscopic intervention is currently being used on patients with high grade dysplasia CRAs, with diameters of >1 cm, or villous components of >25% who are at higher risk than other CRA sufferers. During the process, biopsy samples are taken for conventional histological diagnosis, but poor pathomorphological sensitivity and specificity greatly limit the diagnostic accuracy. Unfortunately, there are no reliable molecular criteria available that can predict the potential development of CRA to CRC. Gene expression profiles of normal colorectal mucosa (NOR), CRA and different Dukes' stages of CRC biopsy specimens, which represent the gradual progress of the CRA to CRC sequence, were determined by Affymetrix technology. Representative regulated genes were further analyzed by quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC). Intersectional analyses of discriminative expression signatures of CRC vs. CRA and CRA vs. NOR allowed the identification of an intermediate signature of 463 probe sets (psets) that mark the NOR--> CRA-->CRC progression. This signature represents a reservoir of candidate markers for the early diagnosis of higher-risk CRA, thus allowing for timely therapeutic intervention and more selective treatment. A further 279 CRC-specific psets pointing to the malignant transition from CRA to CRC were identified and these could represent potential therapeutic targets for CRC. The reliability of the results was further confirmed by qRT-PCR and IHC analyses of the 4-gene sets randomly selected from the 463 psets.