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The past few decades have witnessed scientists gaining a considerable understanding of the molecular pathogenesis of human diseases, especially of cancer. Studies of the molecular basis of carcinogenesis have led to the realization that cancer is fundamentally a disease of genetic alterations. The multiple genetic changes in cancer are predominantly the result of accumulating mutations that have occurred in the genome over time. These genetic changes lead to the production of gene products with upreguated, repressed, or loss of function, which in turn produce aberrant signal transduction pathways and dysregulated cellular functions. The bulk of evidence demonstrates that dysregulated signal transduction pathways promote malignant transformation and support the formation, maintenance and progression of tumors. The initial discovery of viral oncogenes and how these oncogenes could induce malignant transformation, in part by dysregulating growth and survival pathways, has provided us with a strong link between aberrant signal transduction and tumorigenesis. Studies subsequently identified cellular counterparts of oncogenes, called proto-oncogenes, and noted that the functions of these become dysregulated in response to oncogenes and activating mutations harbored in these proto-oncogenes. The presence of activating mutations in proto-oncogenes have been linked to aberrations in signaling intermediates, in turn leading to a perturbed signaling network that drives uncontrolled cell growth and survival, migration, invasion and metastasis, and promoting new blood vessel formation, as well as suppressing tumor immune surveillance. Indeed many human tumors harbor activatingmutations in cellular proto-oncogenes. Multiple molecular alterations in genesa "amplifications, overexpression and/or activating mutationsa "have been found in human tumors that code for proteins with constitutive activity, such as Ras family Gproteins, growth factors and receptors, and tyrosine kinases. Furthermore, tumors with loss-of-function mutations in p53 tumor suppressor gene and others alike have been detected. These critical mutations that create dysfunctional proteins or lead to loss of function of important regulatory proteins permanently alter cellular signaling network and promote cellular behavior consistent with malignant transformation, including anchorage-independent growth and loss of contact inhibition, factor-independent growth, uncontrolled cell cycle, and the possession of survival advantage.
