Purpose: To compare performance of various tumour response criteria (TRCs) in assessment of regorafenib activity in patients with advanced gastrointestinal stromal tumour (GIST) with prior failure of imatinib and sunitinib.
Methods: Twenty participants in a phase II trial received oral regorafenib (median duration 47 weeks; interquartile range (IQR) 24-88) with computed tomography (CT) imaging at baseline and every two months thereafter. Tumour response was prospectively determined on using Response Evaluation Criteria in Solid Tumours (RECIST) 1.1, and retrospectively reassessed for comparison per RECIST 1.0, World Health Organization (WHO) and Choi criteria, using the same target lesions. Clinical benefit rate [CBR; complete or partial response (CR or PR) or stable disease (SD)≥16 weeks] and progression-free survival (PFS) were compared between various TRCs using kappa statistics. Performance of TRCs in predicting overall survival (OS) was compared by comparing OS in groups with progression-free intervals less than or greater than 20 weeks by each TRC using c-statistics.
Results: PR was more frequent by Choi (90%) than RECIST 1.1, RECIST 1.0 and WHO (20% each), however, CBR was similar between various TRCs (overall CBR 85-90%, 95-100% agreement between all TRC pairs). PFS per RECIST 1.0 was similar to RECIST 1.1 (median 44 weeks versus 58 weeks), and shorter for WHO (median 34 weeks) and Choi (median 24 weeks). With RECIST 1.1, RECIST 1.0 and WHO, there was moderate concordance between PFS and OS (c-statistics 0.596-0.679). Choi criteria had less favourable concordance (c-statistic 0.506).
Conclusions: RECIST 1.1 and WHO performed somewhat better than Choi criteria as TRC for response evaluation in patients with advanced GIST after prior failure on imatinib and sunitinib.
Keywords: Choi; Gastrointestinal stromal tumour; RECIST; Regorafenib; Tumour response criteria.
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