On February 27, 2026 Bayer reported results from the ongoing global Phase I first-in-human, dose-escalation PAnTHa study (NCT06217822) evaluating the safety, tolerability and preliminary efficacy of 225Ac-PSMA-Trillium (BAY 3563254), a next-generation targeted alpha therapy (TAT) in patients with advanced metastatic castration-resistant prostate cancer (mCRPC). The dose for expansion was successfully identified, with ≥80% of patients achieving a PSA50 response at the expansion dose.

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New data were presented during the 2026 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Genitourinary Cancers Symposium, taking place in San Francisco, CA, United States, from February 26-28, 2026. These clinical data represent the first disclosure for 225Ac-PSMA-Trillium and were selected as part of the rapid oral session focused on advanced prostate cancer research. They support advancing 225Ac-PSMA-Trillium to the next phase of clinical development. TAT is a strategic pillar of precision oncology at Bayer, with the potential to accelerate novel treatment options for patients with mCRPC.

"We are excited to see the results from the Phase I PAnTHa study demonstrating the potential of our next-generation targeted alpha therapy to provide new treatment options for patients with advanced metastatic castration-resistant prostate cancer (mCRPC), a type of cancer with limited treatment options and poor prognosis," said Dominik Ruettinger, M.D., Ph.D., Head of Research and Early Development for Oncology at Bayer’s Pharmaceuticals Division. "The development of 225Ac-PSMA-Trillium confirms our ongoing focus on prostate cancer treatment and continued drive to develop precise and personalized healthcare solutions."

"Despite progress, patients with metastatic castration-resistant prostate cancer continue to face high mortality, highlighting the urgent need for new precision therapies," said Fred Saad, MD, FRCS, Professor and Chairman of Surgery at the University of Montreal and Director of Genitourinary Oncology at the University of Montreal Hospital Center (CHUM), Canada. "The promising data support the further investigation of this molecule to provide a potentially meaningful clinical benefit for patients with mCRPC."

225Ac-PSMA-Trillium (BAY 3563254) is a next-generation investigational TAT labeled with actinium-225 and comprising a novel PSMA (prostate-specific membrane antigen)-targeting small molecule with a customized albumin-binding moiety. The compound is designed specifically to increase uptake within the tumor, with the goal to provide a differentiated safety and efficacy profile.

Prostate cancer is the second most commonly diagnosed cancer in men with less than three years median survival among metastatic patients, who have developed castration-resistance. There is an increasing unmet need to improve the outcomes of men with mCRPC.6

About the PAnTHa study (NCT06217822)
PSMA-targeted Actinium-225-Trillium FiH study in Advanced mCRPC (PAnTHa), is a Phase I, open-label, first-in-human, multicenter study to evaluate safety, tolerability, pharmacokinetics, and antitumor activity of 225Ac-PSMA-Trillium (BAY 3563254) in participants with advanced metastatic castration resistant prostate cancer (mCRPC) that have at least 1 PSMA-positive lesion on PSMA-PET. In the trial, patients received 225Ac-PSMA-Trillium intravenously every 6 weeks for up to 4 doses. At data cut-off, 50 patients were enrolled across four dose levels in the escalation cohort and 80% completed all four cycles of 225Ac-PSMA-Trillium (range: 75 to 150 kBq/kg; 12-13 patients/cohort).

Detailed Results from PAnTHa
To date, 225Ac-PSMA-Trillium has had no dose-limiting toxicities (DLTs) or treatment-related deaths. Most common treatment-emergent adverse events (TEAEs) were dry mouth, fatigue and nausea. Overall, 38% of patients had Gr ≥3 TEAEs, most commonly lymphopenia, 16% of patients had serious TEAEs and 4% of patients discontinued treatment due to TEAEs. The overall response rate per PCWG3 criteria across all doses in patients with measurable disease at baseline (n=24) was 46%, with disease control rate of 83%. Respective PSA50 and PSA90 response rates were 58% and 36% overall, and 83% and 58% at the Recommended Dose for Expansion (RDE). This was further supported by the decline in circulating tumor DNA (ctDNA) fraction at the RDE. Further, PSA50 responses were observed across all baseline mean Standardized Uptake Value (SUVmean) groups.

About 225Ac-PSMA-Trillium (BAY 3563254)
225Ac-PSMA-Trillium (BAY 3563254) is a next-generation TAT that comprises a highly specific PSMA-targeting motif, an albumin-binding domain to optimize tumor uptake and retention, and a MacropaTM chelator complexed with the alpha-emitter actinium-225. The distinctive structural components are designed to provide a differentiated safety and efficacy profile. Both in vitro and in vivo characterization of 225Ac-PSMA-Trillium demonstrates high tumor uptake and retention. Potent antitumor efficacy has been observed in several preclinical models of prostate cancer. PSMA-Trillium resulted from the acquisition of PSMA Therapeutics and Noria Therapeutics in 2021 and are now under clinical investigation.

About Targeted Alpha Therapy
Targeted alpha therapy (TAT) is an emerging class of radionuclide therapy that can be used against a variety of tumors. It delivers alpha particle radiation directly to the tumor inside the body, either via its bone-seeking property (radium-223) or by combining alpha radionuclides, such as actinium-225, with specific targeting moieties.

Actinium-225 is an alpha particle–emitting radionuclide with a 9.9-day half-life. Alpha particles deposit highly ionizing radiation over a short range. This localized delivery of the radioactive payload induces irreparable DNA double-strand breaks, often resulting in cell death.

About prostate cancer
Prostate cancer is the second most commonly diagnosed cancer in men. Despite significant advances in the last decade, the prognosis for men with mCRPC remains poor with a median survival of about 31 months.2 With increasing incidence, more than 300 thousand prostate cancer cases were reported in the US in 2025; 5-year relative survival with distant disease is only 34%.3 Advances in imaging technologies (i.e. PSMA-PET) and their utilization across all stages of prostate cancer will likely result in an increased number of patients diagnosed with metastatic disease earlier. Consequently, more men will be diagnosed with de novo PSMA-positive metastatic disease.

(Press release, Bayer, FEB 27, 2026, View Source [SID1234663138])