Monte Rosa Therapeutics reported that its updated Phase 1/2 data for the molecular‑glue degrader MRT‑2359 combined with the androgen‑receptor inhibitor enzalutamide showed a 100 % prostate‑specific antigen (PSA) response rate in five heavily pre‑treated metastatic castration‑resistant prostate cancer (mCRPC) patients who carried AR mutations. Two of the five patients achieved a PSA90 response and the remaining three achieved PSA50, while the AR‑mutant subgroup also achieved a 100 % disease‑control rate (DCR). Overall, 67 % of all evaluable patients met RECIST disease‑control criteria, and tumor size reductions were observed in 10 of 15 patients who were assessable for radiographic response.
The updated data build on the December 2025 release, which reported a 100 % PSA response in four of four AR‑mutant patients (two PSA90 and two PSA50) and a 100 % DCR. Expanding the cohort to five patients maintained the same response rates and added RECIST partial responses, demonstrating consistent efficacy as the sample size grows.
These results validate Monte Rosa’s molecular‑glue degrader (MGD) platform in a difficult‑to‑treat population and strengthen the company’s oncology pipeline. The data support the planned confirmatory Phase 2 study of MRT‑2359 plus a second‑generation AR inhibitor, slated to begin in Q3 2026, and provide a clear path toward potential registration of the combination therapy.
Investors reacted positively to the data, with Monte Rosa’s shares gaining 3.9 % in pre‑market trading. The market response was driven by the 100 % PSA response and disease‑control rates in the AR‑mutant subgroup, which represent a significant therapeutic advance in a population with limited options.
"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. Strikingly, in this updated dataset, 5 of 5 patients with AR mutations demonstrated a PSA response, including 2 PSA90 responses and 3 PSA50 responses," said Filip Janku, M.D., Ph.D., Chief Medical Officer of Monte Rosa Therapeutics.
Monte Rosa plans to initiate a confirmatory Phase 2 study of MRT‑2359 plus a second‑generation AR inhibitor in Q3 2026, aiming to validate the clinical activity observed in the Phase 1/2 data and advance the program toward registration.
The combination leverages enzalutamide, an established AR inhibitor, with MRT‑2359’s novel protein‑degradation mechanism. This approach could overcome resistance to conventional AR‑targeted therapies and offers a distinct competitive advantage in the mCRPC market.
Monte Rosa maintains a solid cash balance that is expected to fund operations through 2028, providing the financial runway needed to support the upcoming Phase 2 study and further development of its MGD platform.
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