Drug therapy for GISTs consists of oral medicines called tyrosine kinase inhibitors (TKIs). These are medicines that treat the cause of almost all GISTs—the abnormal KIT protein. TKIs work in GIST by blocking, or turning off, the signal from the KIT protein, which may cause the GIST cells to stop growing. [Note: GISTs that do not have an abnormal KIT protein may also be treated with a TKI, although the choice of drug may be different.]