Overall survival analysis of EXAM, a phase III trial of cabozantinib in patients with radiographically progressive medullary thyroid carcinoma

Abstract

BackgroundPrimary analysis of the double-blind, phase III Efficacy of XL184 (Cabozantinib) in Advanced Medullary Thyroid Cancer (EXAM) trial demonstrated significant improvement in progression-free survival with cabozantinib versus placebo in patients with progressive medullary thyroid cancer (MTC). Final analysis of overall survival (OS), a key secondary endpoint, was carried out after long-term follow-up. Patients and methodsEXAM compared cabozantinib with placebo in 330 patients with documented radiographic progression of metastatic MTC. Patients were randomized (2:1) to cabozantinib (140mg/day) or placebo. Final OS and updated safety data are reported. ResultsMinimum follow-up was 42months. Kaplan–Meier analysis showed a 5.5-month increase in median OS with cabozantinib versus placebo (26.6 versus 21.1months) although the difference did not reach statistical significance [stratified hazard ratio (HR), 0.85; 95% confidence interval (CI), 0.64–1.12; P=0.24]. In an exploratory assessment of OS, progression-free survival, and objective response rate, cabozantinib appeared to have a larger treatment effect in patients with RET M918T mutation–positive tumors compared with patients not harboring this mutation. For patients with RET M918T-positive disease, median OS was 44.3months for cabozantinib versus 18.9months for placebo [HR, 0.60; 95% CI, 0.38–0.94; P=0.03 (not adjusted for multiple subgroup analyses)], with corresponding values of 20.2 versus 21.5months (HR, 1.12; 95% CI, 0.70–1.82; P=0.63) in the RET M918T–negative subgroup. Median treatment duration was 10.8months with cabozantinib and 3.4months with placebo. The safety profile for cabozantinib remained consistent with that of the primary analysis. ConclusionThe secondary end point was not met in this final OS analysis from the trial of cabozantinib in patients with metastatic, radiographically progressive MTC. A statistically nonsignificant increase in OS was observed for cabozantinib compared with placebo. Exploratory analyses suggest that patients with RET M918T–positive tumors may experience a greater treatment benefit with cabozantinib. Trial Registration NumberNCT00704730