First-in-human Study of IDRX-42 in Participants With Metastatic and/or Unresectable Gastrointestinal Stromal Tumors

This is a Phase 1/1b open-label, first-in-human FIH study of IDRX-42, an orally administered small molecule tyrosine kinase inhibitor. Eligible participants will have metastatic and/or surgically unresectable GIST. The study consists of 2 parts. Phase 1 comprises dose escalation to assess clinical and pharmacologic profile and safety/tolerability after failure of at least prior imatinib and support choice of the recommended phase 1b dose(s) and schedule(s) (RP1bDs)). Phase 1b expansion will enroll separate cohorts of participants defined by numbers of lines of prior GIST therapy at the selected RP1bD(s) to assess the preliminary antitumor effect of IDRX-42 and further characterize the safety profile of IDRX-42 at the RP1bD(s). In addition, a Concentration-QTc (C-QTc) substudy will be conducted in a subset of participants enrolled at selected sites in the study to characterize the effects of IDRX-42 on QTc and other ECG parameters in GIST patients.