Monte Rosa Reports 100% PSA Response in AR-Mutant mCRPC; Phase 2 Set for Q3 2026
Monte Rosa’s MRT-2359 plus enzalutamide produced a 100% PSA response in 5 AR-mutant mCRPC patients and a 67% RECIST disease control rate with 10 of 15 patients showing lesion reductions. Adverse events were mainly Grade 1-2 with no discontinuations, and Phase 2 is planned for Q3 2026.
1. Clinical Efficacy Data
Data from 15 evaluable mCRPC patients showed a 67% RECIST disease control rate overall, with 10 showing measurable tumor reductions. In the AR-mutant subgroup, all 5 patients achieved PSA responses, including two RECIST partial responses and three with stable disease.
2. Safety and Tolerability
The MRT-2359 and enzalutamide combination was generally well-tolerated, with most treatment-related adverse events classified as Grade 1-2 fatigue, diarrhea, nausea and decreased appetite. No patients discontinued therapy due to adverse events.
3. Planned Phase 2 Study
The company plans to initiate a signal-confirming Phase 2 study in Q3 2026 targeting AR-mutant mCRPC patients, using a two-stage design to evaluate efficacy in up to 25 patients prior to registrational studies.