Mechanisms of the resistance of gastrointestinal stromal tumors to imatinib

The review describes the modern concepts of the primary and secondary (acquired) resistance of gastrointestinal stromal tumors to the targeted drug imatinib. Gastrointestinal stromal tumors are the mesenchymal tumors of gastrointestinal tract that originate from interstitial cells of Cajal or their stem cell precursors. Up to 85 % of gastrointestinal stromal tumors have the mutations of KIT gene that lead to ligand-independent activation of this tyrosine kinase. Imatinib is an inhibitor of KIT tyrosine kinase which is hyperexpressed in 70-85 % of cases on the cell membrane of gastrointestinal stromal tumors. Despite the high effectiveness of imatinib in gastrointestinal stromal tumors, up to 15 % of patients do not respond to this therapy, and over 50 % of patients acquire the resistance to this drug 2 years after initiation of target therapy with imatinib. The mechanisms of primary resistance include basically the mutational status of KIT, PDGFRA and, rarely, mutations of SDH, NF1, BRAF, PI3K3CA, CBL, and KRAS. The mechanisms of secondary resistance of tumor cells to imatinib are not restricted to the secondary mutations of KIT and PDGFRA, but also might be due to the loss of KIT expression associated by overexpression of the alternative receptor- and non-receptor tyrosine kinases, such as MET, AXL, FGFR2α, FAK, etc. Alternative mechanisms of acquired resistance might be due to the mutations of BRAF gene.