Response of gastrointestinal stromal tumors (GISTs) to imatinib by Choi criteria and response evaluation criteria in solid tumors (RECIST) as surrogates for survival and time to progression

Abstract

9506 Background: Recent studies have demonstrated that RECIST is insensitive in evaluating GIST’s treated with imatinib. We have demonstrated in a small group of patients that a good response by Choi Criteria, i.e., a 10% decrease in unidimensional tumor size or a 15% decrease in tumor density on contrast-enhanced CT, correlated well with good response by PET (Proc. ASCO 22:819, 2003) and was more predictive of time to tumor progression (TTP) than response by RECIST (CTOS 2004). The aim of this study was to validate the correlation with disease-specific survival (DSS) and TTP with follow-up updated to 5-years. Methods: We evaluated 98 patients treated with imatinib for recurrent or metastatic GIST at our institution from December 2000 to September 2001 by RECIST and Choi criteria. All patients had pre-treatment and initial 2-monthly follow-up CT’s. DSS and TTP were analyzed by response category. Results: There were 28 (48%) good responders by RECIST and 30 (52%) poor responders. There were 49 (84%) good responders by Choi criteria, and 9 (16%) poor responders. Patients with good response by Choi criteria on CT at 8 weeks after treatment had significantly improved DSS (P = 0.04) in contrast to those with complete or partial response at any time by RECIST (P = 0.45). Similarly, TTP was significantly correlated with Choi response group (P = 0.01) but not with response group by RECIST (P = 0.74). Conclusions: Choi response criteria, incorporating tumor density and using small changes in tumor size on CT, are more sensitive and more accurate than RECIST in assessing the response of GISTs to imatinib mesylate and should be routinely incorporated into future studies of GIST therapy. Good response is detected earlier by Choi criteria and is a valid surrogate for DSS and TTP. We should desist using RECIST, at least in GIST. (Supported in part by NCI contracts U01-CA70172–01 and N01-CM-17003) [Table: see text]