• BLU-285 was updated to the newly approved generic name, avapritinib, and the stratification of subjects by mutation status was updated from Platelet-derived growth factor receptor alpha (PDGFRA) vs V-Kit Hardy-Zuckerman 4 Feline Sarcoma Viral Oncogene Homolog (KIT) to PDGFRA D842V mutation present or absent. • Study Objectives, Study Endpoints, and related sections of the Study Summary were updated and reorganized in response to feedback from the FDA. • Study Conduct, related sections of the Study Summary, and all other related sections of the protocol were updated to clarify the circumstances where avapritinib doses could be escalated from 300 mg QD to 400 mg QD, to specify that a washout period was required for Subjects who switched from treatment with regorafenib to treatment with avapritinib, and to provide additional details for avapritinib dose reductions and re-escalations.

• Inclusion criterion, the subjects with ECOG PS of 2 were no longer to be included. • The Subjects with arterial thrombotic or embolic events within 6 months or venous thrombotic events within 14 days before randomization were excluded. • Exclude subjects with a brain aneurysm if it had not been removed or repaired. • Exclude subjects with known hypersensitivity to avapritinib, regorafenib, or the excipients in either study drug as a precautionary measure.

Key modifications made to the protocol as a part of Amendment 3, are summarized below. • The planned interim analysis was removed in order to provide more mature PFS and OS data at the time of primary analysis of efficacy. This also allowed enrollment of an adequate number of patients in Asia. • The EORTC-QLQ-C30 physical functioning, pain, role functioning, and appetite loss scores were moved from key secondary to secondary objectives and endpoints and were no longer in the hierarchy of the sequential testing scheme. • Removed from the exploratory objectives and corresponding endpoints the correlation of clinical efficacy with other cancer-relevant gene mutant allele fractions and mutant allele fractions measured in ctDNA • Removed the option of escalating the avapritinib dose to 400 mg QD based on analyses of safety showing earlier onset and higher-grade AEs at 400 mg dose versus 300 mg dose. • Added in Section, Prohibited Concomitant Therapy, that patients who experienced centrally confirmed disease progression but subsequently underwent radiation therapy or surgery may continue to receive study treatment with avapritinib, if the treating investigator considered it to be in the patient’s best medical interest. • Added brain imaging assessments at Week 12 (± 1 week) and Week 24 (± 1 week), and instructions to repeat as clinically indicated, ie, for unexpected neurologic AEs, in response to feedback from regulatory authorities. • Updated language used for AE and SAE definitions, recording, and reporting. • Removed the requirement that patients underwent at least 1 postbaseline tumor assessment by independent radiology reviewers to be included in the per-protocol population.