A Study of Velzatinib in Participants With Metastatic and/or Unresectable GIST After Imatinib, Sunitinib, Regorafenib, and Pimitespib

Inclusion Criteria: * Histologically or cytologically confirmed GIST that is metastatic and/or surgically unresectable. * Documented disease progression on or intolerance to imatinib, sunitinib, regorafenib, and pimitespib. * Documented mutation status of KIT and/or PDGFRA. * Tumor tissue may be available for retrospective biomarker analysis. The sample may be from archival tissue or a new biopsy. Investigators may consult with the sponsor regarding the enrolment of participants for whom archival tissue is no longer available and who are not eligible to undergo a new biopsy. * Is willing to use adequate contraception male and/or female participants. Exclusion Criteria: * Known untreated or active central nervous system metastases. * Has significant, uncontrolled, or active cardiovascular disease. * Participants with a known allergy or hypersensitivity to any component of velzatinib. Participants with a history of Stevens-Johnson syndrome on a prior Tyrosine kinase inhibitor (TKI) are excluded. * Has a malignancy (except disease under study) that has progressed or required active treatment within the past 24 months except for basal cell or squamous cell carcinomas of the skin or in-situ carcinomas \[e.g., breast, cervix, bladder\] that have been resected with no evidence of metastatic disease. * Prior treatment with ripretinib or other investigational agents that are currently under clinical development for GIST. * Is pregnant or breastfeeding. * Any condition or illness that, in the opinion of the Investigator, might compromise participant safety or interfere with the evaluation of the safety of the study treatment.