445PD - Clinical Activity and Pharmacokinetics (PK) of Cabozantinib (XL184) in Patients with Progressive Medullary Thyroid Carcinoma (MTC)

Abstract

ABSTRACT Background Cabozantinib (cabo) is a potent oral therapy that inhibits MET, VEGFR2, and RET. In a phase 1 study, cabo demonstrated anti-tumor activity in patients with MTC, and a long terminal half-life of 120 hours. We report clinical activity and PK analyses from a Phase 3 study of cabo versus placebo (P) in patients with progressive, unresectable, locally advanced or metastatic MTC. Methods Patients with MTC and documented RECIST progression within 14 months (mo) of screening were randomized 2:1 to receive cabo (140 mg freebase qd, n = 219) or placebo (n = 111). Blood samples for PK were collected on days 1 and 29. Baseline tumor and blood samples were evaluated for RET mutation status. Tumor assessments occurred every 12 weeks, and the primary efficacy measure was progression-free survival (PFS), assessed by an independent radiology committee using RECIST. Results Statistically significant PFS prolongation was observed, with median PFS for cabo of 11.2 mo versus 4.0 mo for P (HR 0.28, 95% CI 0.19-0.40, p Conclusions Cabo significantly prolonged PFS compared to placebo in a patient population with progressive MTC. PK analysis supports administration of cabo as a fixed dose without adjustment for patient covariates. Disclosure M.J. Schlumberger: MJ Schlumberger has been a compensated consultant for Exelixis. M. Brose: Dr. Brose has received research funding and honoraria from Exelixis. M. Shah: Dr. Shah has received research funding from Exelixis. D.R. Miles: D. Miles is an employee and stockholder of Exelixis. L.T. Nguyen: Linh Nguyen is an employee and stockholder in Exelixis. S. Sherman: Dr. Sherman is a compensated consultant to Exelixis. All other authors have declared no conflicts of interest.