Expression of c-myc and c-fos mRNA in colorectal carcinoma in man

Thirty colorectal carcinomas, 1 adenoma of the colon, 1 case of Crohn's disease and 13 specimens of non-neoplastic colorectal mucosa were examined for qualitative and quantitative expression of the c-myc and c-fos protooncogenes. These genes encode nuclear proteins, which are both believed to regulate gene transcription. Oncogene expression was evaluated at the mRNA level by in situ hybridization and Northern blot analysis. Densitometric analysis of the specific bands on Northern blots revealed a highly significant overexpression of c-myc mRNA in colorectal carcinomas compared with non-neoplastic tissue (p less than 0.001). Furthermore, increased expression of c-myc mRNA was found in moderately and poorly differentiated carcinomas compared with well differentiated ones. In contrast to c-myc, c-fos mRNA expression was significantly lower in carcinomas than in non neoplastic tissue (p less than 0.02). Neither, c-myc nor c-fos mRNA levels showed a clear-cut correlation with tumor stage. We conclude that c-myc mRNA overexpression plays an important role in the progression of colorectal carcinomas. In contrast enhanced c-fos mRNA expression may be related to cell differentiation, both in tumors and non-neoplastic tissue.