Which is the molecular mechanism underlying K-ras alterations in carcinomas?
['activating mutations in KRAS are identified in most pancreatic cancers', 'Mutations at codon 12 of the K-ras gene are present in 65%-100% of carcinomas of human exocrine pancreas and could be used as a potential tumor marker at the tissue level.', 'Activating point mutations in the K-Ras oncogene are among the most common genetic alterations in pancreatic cancer, occurring early in the progression of the disease.', 'Activating K-ras mutations are found in approximately 90% of pancreatic carcinomas and may contribute to the poor prognosis of these tumors.', 'Five of the seven duct lesions harbored activating point mutations in codon 12 of K-ras; a G to A transition was found in four and a G to C transversion in one.', 'Ki-RAS mutations in 38% of the overall series', 'KRAS exon 2 mutations were detected in a total of 62 patients with the two methods combined, comprising 11 different mutant alleles.', 'gain-of-function mutations in ras genes were the first specific genetic alterations identified in human cancer']
['Activating point mutations most frequently in codon 12']
['Point mutations']