08:43 AM EDT, 05/13/2025 (MT Newswires) -- GSK (GSK) and iTeos Therapeutics ( ITOS ) said Tuesday they are ending the development program for belrestotug as two phase 2 cancer studies failed to meet the efficacy criteria for continued development.

The companies said that as a result, they are ending their collaboration and all belrestotug-containing study groups.

ITeos said the study evaluating the belrestotug plus dostarlimab doublet in previously untreated, unresectable, locally advanced or metastatic PD-L1 high non-small cell lung cancer didn't meet established criteria for clinically meaningful improvements in the secondary endpoint of progression-free survival.

The company added that the other trial showed a trend lower than the meaningful threshold for objective response rate in the belrestotug combination groups compared with dostarlimab monotherapy in PD-L1 positive head and neck squamous cell carcinoma.

The company said any new enrollment in an ongoing phase 3 trial is ending, adding that GSK is reaching out to various parties about the next steps for proper management of currently enrolled patients.

ITeos said it is taking steps to preserve capital and has started a process to look for opportunities that preserve and maximize shareholder value.

Shares of iTeos rose 18% and GSK fell 1.5% in premarket activity Tuesday.