Purpose: Gastrointestinal stromal tumor (GIST) is a relatively rare tumor that is treated with targeted therapies in advanced stages. Randomized clinical trials (RCT) often require long followup and large sample sizes to evaluate overall survival (OS), the gold-standard measure of treatment efficacy. However, changes in therapy following disease progression may complicate survival assessments. Establishing surrogate endpoints may facilitate the drug approval and availability of new efficacious treatments; however, no published studies have investigated this topic in unresectable and/or metastatic GIST.Experimental Design: A systematic literature review identified 14 RCTs and five observational studies of sufficient methodologic quality published between January 1995 and December 2013 (29 treatment arms; 2,189 patients). Weighted linear regression was used to evaluate the relation between median OS and median progression-free survival (PFS) for all arms combined and stratified by treatment line, treatment type, and quality score.Results: Median OS and PFS were positively related with a correlation of 0.91. The association was still moderate (correlation 0.72) after eliminating four influential data points. In stratified analyses, correlation of OS and PFS was greater in later lines of therapy (first line ¼ 0.52; second line ¼ 0.80; third-and laterline ¼ 0.70) and imatinib showed a stronger association (0.91) than other evaluated treatments (À0.26 to 0.69).Conclusion: This analysis identified a strong relationship between median OS and PFS, especially in later lines of therapy. Findings suggest that PFS could serve as a surrogate marker for OS; however, analyses of patient-level data are needed to establish its validity in GIST.

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578 Background: There is an unmet need for treatments that provide a survival benefit for patients with heavily pretreated metastatic colorectal cancer (mCRC). In a randomized, double-blind, placebo-controlled trial, patients treated with regorafenib plus best supportive care (BSC) had significant improvement in overall survival (OS) versus patients in the placebo arm receiving BSC alone. The aim of this study was to estimate the cost-effectiveness of regorafenib for the treatment of patients with mCRC after failure or intolerance to irinotecan-, oxaliplatin-, and fluorouracil-based regimens, from the perspective of a U.S. health care payer. Methods: A cohort-partition model was developed to simulate treatment costs and survival for patients treated with regorafenib or BSC alone. Survival was projected by fitting Weibull distributions to trial data. Mean duration of treatment (3.0 months regorafenib, 2.1 months BSC), utilities (0.71 on treatment, 0.59 post-treatment) and serious adverse event rates were also based on trial data. Monthly drug monitoring and physician fee costs were based on Medicare fee schedules. Routine mCRC care and adverse event unit costs were obtained from an analysis of administrative claims in two large managed care databases. Costs were estimated in 2012 USD. Results: Patients treated with regorafenib had prolonged survival versus BSC alone (0.75 versus 0.60 years) and also had higher lifetime costs ($97,700 versus $59,494). The improvement in quality-adjusted life years (0.47 versus 0.37) was small due to the heavily pretreated nature of the patient population. The increase in costs was attributable to increases in costs for drug acquisition, adverse events , and routine care from increased survival. Conclusions: Regorafenib increases life expectancy for patients with pretreated metastatic colorectal cancer. The cost of this benefit could be considered high; however, it could be justifiable given high unmet need for these patients. The increase in cost is primarily due to drug acquisition costs, similar to other recent treatments for metastatic cancers.