Overexpression and amplification of c-myc during progression of human colorectal cancer

Overexpression and amplification of the c-myc oncogene occur in approximately 70 and 10% of human primary colorectal carcinomas, respectively, indicating the importance of this gene in colorectal tumorigenesis. Little, however, is known about the involvement of c-myc in the progression of colorectal cancer. We therefore determined c-myc gene expression and amplification in a group of primary tumors and metastases from patients with colorectal cancer using quantitative PCR-based tests. While the percentage of metastases overexpressing c-myc (13/26 = 50%) was in the same range as reported for primary tumors by others, gene amplification of c-myc was significantly (p = 0.001) more frequent in metastases (16/27 = 59%) compared to primary tumors (1/23 = 4%) in our series. Interestingly, in 23 metastases where both expression and amplification of c-myc could be determined, there was no correlation between gene copy number and expression level (p = 0.18; r = 0.19). We conclude that amplification but not overexpression of c-myc is related to metastatic progression of colorectal cancer and that overexpression of c-myc is driven by mechanisms other than the number of c-myc copies in the tumors studied.