Kinase mutations and imatinib mesylate response for 64 Taiwanese with advanced GIST: Preliminary experience from Chang Gung Memorial Hospital

Purpose: Most gastrointestinal stromal tumors (GISTs) express constitutively activated mutation of kit or platelet-derived growth factor receptor alpha (PDGFRA), which are therapeutic targets for imatinib. Results of 64 Taiwanese with advanced GIST treated with imatinib were reported. Method and materials: Between 2001 and May 2006, a prospective, non-randomized, and a single center trial containing 64 Taiwanese patients with advanced GIST treated with imatinib was conducted. Each tumor was investigated for mutations of kit or PDGFRA. Results: The median follow-up time after imatinib administration was 16.1 months. 12 patients (18.8%) had complete response (CR), 24 (37.5%) had a partial response (PR), 12 stationary disease (18.8%), 16 progressive disease (25.0%). The 64 Taiwanese with advanced GIST had an estimated median survival of 48.0 months and 4-year survival rate for 76.1%. Kit mutation was found in 49 of 54 (90.7%) test patients and five of them had no mutation (9.3%). No PDGFRA mutant was identified. In 40 patients harboring kit exon 11 mutations, the CR and PR rates (ORR) were 57.5% , nine patients with tumors containing kit exon 9 mutation had ORR rates of 22.2%, and five patients with no mutation had ORR rates of 60.0% (not significant; P = 0.149). Conclusions: Activated mutation of kit constituted 90.7% genetic alteration of Taiwanese with advanced GIST and no PDGFRA mutation was detected. Imatinib induced a sustained objective response in more than half of Taiwan advanced GIST patients. ORR did not differ between patients whose GISTs had no mutation, kit exon 9, and 11 mutations.