Phase 2 Study to Evaluate the Efficacy of Regorafenib in Specific GIST Mutation Subsets (KIT Exon 17, 18, or 14 Mutation and SDHB Deficient GIST) in the Post-imatinib Second-line Setting.

Primary Objectives:

To assess efficacy of regorafenib in second-line GIST for patients with KIT exon 17, 18, or 14 mutation and SDHB deficient who progressed on imatinib as measured by PFS (RECIST 1.1).

Secondary Objectives:

1. RR by RECIST 1.1 and CHOI criteria 2. Progression-free rate at 1 year and 2 years 3. Median OS and OS at 1 years, 2years, and 5 years

Exploratory objectives:

1. Resistance mechanism (ctDNA analysis) in patients initially responding to regorafenib 2. Response data on next line of treatment post regorafenib