Colorectal carcinomas(CRCs)are frequently found in industrialized countries and lead to a high incidence of malignancy-related mortality.Defined by histomorphological features,CRCs and their pre-invasive lesions are quite heterogeneous.The underlying molecular mechanisms include genomic instability,genomic mutation of tumor suppressor genes or oncogenes,epigenetic changes,and the microRNA network.The molecular mechanisms are guided by repeated clonal selections.The genotype-to-phenotype relation is assumed to be the great challenge of cancer research and the development of effective targeted therapies.At present a strong genotype-to-phenotype relation is characterized only for a minority of CRCs.Consequently,the molecular characterization of CRCs is essential to interpret histological patterns and to identify prognostic groups as well as patients for targeted therapy. Colorectal carcinomas (CRCs) are frequently found in industrialized countries and lead to a high incidence of malignancy-related mortality. Deficiency by histomorphological features, CRCs and their pre-invasive lesions are quite heterogeneous. The underlying molecular mechanisms include genomic instability, genomic mutation of tumor suppressor genes or oncogenes, epigenetic changes, and the microRNA network.The molecular mechanisms are guided by repeated clonal selections. The genotype-to-phenotype relation is assumed to be the great challenge of cancer research and the development of effective targeted therapies. At present a strong genotype-to-phenotype relation is characterized only for a minority of CRCs.Consequently, the molecular characterization of CRCs is essential to interpret histological patterns and to identify prognostic groups as well as patients for targeted therapy.