[Responses to treatment and switching tyrosine kinase inhibitors in gastrointestinal stromal tumor(GIST)].

GIST is driven by a gain-of-function mutation either in the KIT or PDGFRA gene. Atpresent , advanced and/or metastatic GIST is primarily treated by medical therapy of imatinib and sunitinib, both of which are re-imbursed by the government in Japan. Tumor responses are usually evaluated by contrast-enhanced CT scan with RECIST criteria, which cannot always predict patients with long SD showing similar prognostic effects to CR or PR. For early detection of drug activities, Choi's criteria with enhanced CT scan, as well as FDG-PET(or PET-CT), are considered to be useful. Choi's criteria also works for the early detection of resistance. When resistance and/or unmanagable adverse events are observed, early switching of drugs without any delay is recommended if there is another line of treatment.