Monte Rosa Therapeutics Presents Positive Phase 1/2 Data for MRT-2359 in Prostate Cancer

Combination with enzalutamide shows 100% PSA response rate in patients with AR mutations

Published on Feb. 24, 2026

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Monte Rosa Therapeutics announced updated positive clinical data from an ongoing Phase 1/2 study evaluating MRT-2359 in combination with enzalutamide in heavily pretreated patients with metastatic castration-resistant prostate cancer (mCRPC). The data showed a 100% PSA response rate and 100% disease control rate in patients with androgen receptor (AR) mutations, including 2 partial responses and 3 with stable disease. The combination was generally well-tolerated, and the company plans to initiate a new Phase 2 study in Q3 2026 to further evaluate MRT-2359 in mCRPC patients with AR mutations.

Why it matters

The data reinforce the potential of MRT-2359 in mCRPC patients with AR mutations, a population with limited therapeutic options. The combination of MRT-2359 and enzalutamide demonstrated promising efficacy and a favorable safety profile, supporting further development of this approach.

The details

In the Phase 1/2 study, 23 heavily pretreated mCRPC patients received MRT-2359 in combination with enzalutamide. Of the 15 evaluable patients, 5 had AR mutations and all 5 showed PSA responses, including 2 with PSA90 responses. The overall RECIST disease control rate was 67%, and 10 of 15 patients had tumor size reductions. The combination was generally well-tolerated, with primarily Grade 1-2 adverse events.

  • The data cutoff date for the analysis was January 30, 2026.
  • The poster presentation will be on February 26, 2026 at the ASCO Genitourinary Cancers Symposium.

The players

Monte Rosa Therapeutics

A clinical-stage biotechnology company developing molecular glue degrader (MGD)-based medicines.

Filip Janku, M.D., Ph.D.

Chief Medical Officer of Monte Rosa Therapeutics.

MRT-2359

An investigational, orally bioavailable, GSPT1-directed MGD discovered and developed by Monte Rosa.

Enzalutamide

An androgen receptor (AR) inhibitor used in combination with MRT-2359 in the Phase 1/2 study.

Metastatic castration-resistant prostate cancer (mCRPC)

The advanced, difficult-to-treat form of prostate cancer that was the focus of the study.

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What they’re saying

“These data bolster the promising results we shared in December, continuing to reinforce MRT-2359's potential in mCRPC patients with AR mutations, a population with limited therapeutic options.”

— Filip Janku, M.D., Ph.D., Chief Medical Officer of Monte Rosa Therapeutics (Monte Rosa Therapeutics)

What’s next

Monte Rosa plans to initiate a new, signal-confirming Phase 2 study of MRT-2359 targeting AR mutant patients in Q3 2026.

The takeaway

The positive results from the Phase 1/2 study of MRT-2359 in combination with enzalutamide in heavily pretreated mCRPC patients, particularly the 100% PSA response rate in patients with AR mutations, demonstrate the potential of this approach to address an unmet need in a difficult-to-treat population.