US pharmaceutical company Merck & Co Inc (NYSE:MRK), known as MSD outside the US and Canada, and its Japanese partner Eisai Co Ltd (TYO:4523) announced on Tuesday that the Phase 3 LITESPARK-011 trial of WELIREG (belzutifan) combined with LENVIMA (lenvatinib) met one of its primary endpoints of progression-free survival (PFS) in patients with advanced renal cell carcinoma (RCC) whose disease progressed after prior anti-PD-1/L1 therapy.

At a pre-specified interim analysis, the combination demonstrated a statistically significant and clinically meaningful improvement in PFS and objective response rate compared with cabozantinib. A trend toward improved overall survival, the study's other primary endpoint, was observed but did not reach statistical significance at this stage.

Safety results for the combination were consistent with known profiles for the individual agents, and no new safety concerns emerged. Merck and Eisai plan to discuss these findings with global regulatory authorities and present the data at an upcoming medical meeting.

LITESPARK-011 represents the first positive Phase 3 study of a HIF-2 alpha inhibitor combined with a multi-targeted VEGF tyrosine kinase inhibitor. The results further expand the late-stage development programme for WELIREG across multiple tumour types, including ongoing evaluation in first-line advanced RCC through the LITESPARK-012 trial.