Monte Rosa’s MRT-2359 Delivers 100% Response in AR-Mutant Prostate Cancer—Next Phase 2 Study Set for 2026

Clinical Results Highlight 100% Disease Control in Challenging Patient Group

Monte Rosa Therapeutics (NASDAQ: GLUE) has released interim clinical data showing that MRT-2359, in combination with enzalutamide, achieved a remarkable 100% PSA response and disease control rate in metastatic castration-resistant prostate cancer (mCRPC) patients harboring androgen receptor (AR) mutations. These results come from a heavily pretreated population—patients with few remaining treatment options—and spotlight the promise of MRT-2359 in advancing the treatment landscape for this difficult-to-treat cancer type.

Efficacy Standout: Compelling Results in AR-Mutant Subgroup

Of 14 evaluable mCRPC patients in the Phase 1/2 trial, 4 were identified with AR mutations. Every one of these patients demonstrated a positive PSA response (2 PSA90, 2 PSA50), with two showing RECIST partial responses and the other two maintaining stable disease. In this subgroup, both PSA response and overall disease control reached 100%. This outcome is notable given that most of these patients had previously undergone treatments such as chemotherapy, radioligand therapy, or even experimental bispecific antibodies.

Favorable Safety and Durable Responses Underpin Next Steps

Safety remains a positive story: the majority of adverse events in the trial were classified as mild to moderate (Grade 1 or 2), predominantly affecting the gastrointestinal tract. Importantly, durability was observed—especially in patients with AR mutations or those who were treatment-naive to AR inhibitors.

The promising safety and efficacy signal led Monte Rosa to announce a forthcoming signal-confirming Phase 2 study, set to start in 2026. The new trial will target up to 25 mCRPC patients with AR mutations, with an eye on expanding into broader patient populations based on interim findings.

Mechanism Insights: Beyond AR—MYC and E2F Pathways Modulated

Researchers also found that MRT-2359 exerts its impact through multiple cancer-driving pathways, not just by inhibiting AR signaling. Analysis of patient tumor samples revealed modulation of the MYC and E2F signaling axes, providing support for a broader anti-tumor mechanism—a finding consistent with earlier preclinical models.

Looking Ahead: ASCO Presentation and Expansion Plans

Investors and the scientific community will want to watch for updated MRT-2359 data to be presented at the ASCO Genitourinary Cancers Symposium in February 2026. With a Phase 2 launch planned and a focus on AR-mutant mCRPC patients—a group with critical unmet needs—the trajectory of this clinical program will be important for both the biotech field and prostate cancer therapy at large.

Quick Reference: Key Details from MRT-2359 Combination Study

Key Takeaway: Phase 2 Could Solidify MRT-2359’s Role in AR-Mutant Prostate Cancer

While further studies and regulatory milestones lie ahead, these early findings place MRT-2359 as a candidate worth tracking in mCRPC, particularly for patients with AR mutations. The clinical and mechanistic evidence—coupled with a manageable safety profile—sets the stage for more robust exploration in upcoming trials. For stakeholders and patients alike, Monte Rosa’s ongoing research could reshape future options in advanced prostate cancer treatment.

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