KIT and gastrointestinal stromal tumor: Progression can be caused by primary resistance to imatinib, in which GIST continues to progress despite the institution of therapy, or by acquired resistance to the TKI, mostly due to the acquisition of secondary mutations in KIT or PDGFRA, interfering with the inhibitory effect of imatinib (Antonescu et al., 2005; Wardelmann et al., 2006).