A Study of IDRX-42 (GSK6042981) Versus (vs) Sunitinib in Participants With Gastrointestinal Stromal Tumors After Imatinib Therapy

Inclusion Criteria: * Participants with histologically or cytologically confirmed GIST that is metastatic and/or surgically unresectable. * Documented disease progression on or intolerance to imatinib administered for first-line treatment of unresectable/metastatic disease. * Documented mutation status of KIT and/or PDGFRA using a tissue based next-generation sequencing or polymerase chain reaction (PCR) assay. * Tumor tissue must be available for retrospective biomarker analysis. Sample may be archival or new biopsy. Exclusion Criteria: * GIST that is both KIT and PDGFRA wild-type or known to harbor an activating PDGFRA exon 18 mutation. * Known untreated or active central nervous system metastases. * Participants with a known allergy or hypersensitivity to any component of IDRX-42 (GSK6042981) or sunitinib. 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.