Among 102 archival tumor tissue samples and 163 plasma samples at baseline from patients included in the phase III GRID study in patients with GIST treated by regorafenib versus placebo, following failure of at least imatinib and sunitinib, Demetri et al. first reported a concordance rate of 100% and 71% between plasma and tissue biopsies for primary KIT exon 9 and 11 mutations, respectively [101]. This evidence concerns the gene KIT and gastrointestinal stromal tumor.