An international, double-blind, randomized, placebo-controlled phase III trial (EXAM) of cabozantinib (XL184) in medullary thyroid carcinoma (MTC) patients (pts) with documented RECIST progression at baseline.

Abstract

5508 Background: MTC arises from parafollicular cells of the thyroid gland, accounts for 5-8% of thyroid cancers and represents an unmet medical need. Cabozantinib (cabo) is an oral inhibitor of MET, VEGFR2, and RET. We conducted a phase III study of cabo vs placebo (P) in pts with progressive, unresectable, locally advanced or metastatic MTC. Methods: Eligible pts were required to have documented RECIST progression within 14 months of screening. The primary efficacy measure was progression-free survival (PFS) as assessed by an independent review facility (IRF) using RECIST. Secondary efficacy measures included objective response rate (ORR) and overall survival (OS). The study has 90% power to detect a 75% increase in PFS and 80% power to detect a 50% increase in OS. Tumor assessments occurred every 12 weeks. Crossover between treatment arms was not allowed. Results: Between Sept 2008 and Feb 2011, 330 pts (median age 55 yrs; 67% male; 96% measureable disease; RET mutation status: pos 48%; neg 12%; unknown 39%; prior TKI exposure: yes 21%, no 78%, unknown 2%) were randomized 2:1 to cabo (140 mg free base [175 mg salt form] qd; n=219) or P (n=111). The planned primary PFS analysis included events through the date of the 138th event. As of 15June2011, 44.7% of pts on cabo and 13.5% on P were still receiving study treatment. Statistically significant PFS prolongation of 7.2 mo was observed; median PFS for cabo was 11.2 mo vs 4.0 mo for P (HR 0.28, 95% CI 0.19-0.40, p<0.0001). PFS results favored the cabo group across subset analyses including RET status and prior TKI use. ORR was 28% for cabo vs 0% for P (p<0.0001). An interim analysis of OS (44% of the 217 required events) did not show a difference between cabo and P. The most frequent grade ≥3 adverse events (cabo vs P) were diarrhea (15.9 vs 1.8%), palmar-plantar erythrodysesthesia (12.6 vs 0%), fatigue (9.3 vs 2.8%), hypocalcemia (9.3 vs 0%), and hypertension (7.9 vs 0%). Conclusions: This phase III study met its primary objective of demonstrating substantial PFS prolongation with cabo vs. P in a patient population with MTC and documented progressive disease in need of therapeutic intervention.