[Clinical and pathological significance of the genetic analysis in colorectal carcinomas]

The molecular genetics of colorectal carcinomas are among the best understood of common human cancers. Three inter-related molecular pathways are involved. The chromosomal instability pathway begins with inactivation of the APC/beta-catenin genes followed by activation of oncogenes and inactivation of additional suppressor genes, commonly with high frequency of allelic losses, cytogenetic abnormalities. The microsatellite instability pathway begins with inactivating one of a group of genes responsible for DNA nucleotide mismatch repair leading to extensive mutations in both repetitive and non-repetitive DNA sequences with low frequencies of allelic losses and rare alteration of tumor DNA content. Finally, the CpG island methylation pathway involves inactivation of genes by methylation of cytosines in promoter regions to silence gene expression without DNA sequence alterations. Molecular genetics have the potential for clinical applications. Combination of genetic classification of high levels of microsatellite instability (MSI-H), gene expression analysis of mismatch repair genes and subsequent mutation analysis of inactivated genes can be used as an effective method for the identification of hereditary nonpolyposis colorectal carcinoma patients. Molecular genetic alterations have been proposed to be of prognostic value, including allelic deletion on chromosome 18q, and on chromosome 17p. MSI-H has been reported as a marker for better prognosis. Individualizing chemoradiation by use of predictive markers for response or resistance to therapy is important in patients with advanced disease or candidacy for adjuvant therapy.