Telix's TLX591-Tx posts 8.8-month rPFS in small Phase 1 mCRPC study
A peer-reviewed publication reports secondary efficacy and safety data from a 30-patient dosimetry study, work Telix now cites in support of its ongoing Phase 3 ProstACT Global trial.
Executive Summary
- Telix published peer-reviewed results from its completed Phase 1 dosimetry and safety study of TLX591-Tx, reporting an rPFS figure that the company is using to support its ongoing later-stage prostate cancer program.
- The study's registered purpose was to characterize biodistribution, radiation dosimetry and safety, not to establish efficacy, so the rPFS result is a secondary finding drawn from a small, uncontrolled cohort.
- TLX591-Tx enters a prostate cancer field crowded with PSMA-targeted radiopharmaceuticals, including a commercially approved rival and a deep bench of Phase 3 programs testing the same target and modality.
- The publication adds a data point management can cite toward its Phase 3 registrational trial, but the readout that will actually test efficacy under randomized conditions has not yet reported.
The catalyst
Telix Pharmaceuticals Limited announced on July 21, 2026 that the ProstACT SELECT study of TLX591-Tx (lutetium-177 rosopatamab tetraxetan) was published in Cancers, a peer-reviewed journal. The Phase 1 trial, registered as NCT04786847, enrolled 30 patients with advanced metastatic castration-resistant prostate cancer (mCRPC) in Australia and completed in February 2024. The publication reports a median rPFS of 8.8 months in evaluable patients treated with TLX591-Tx plus standard of care, along with dosimetry findings the authors describe as low salivary gland irradiation and prolonged tumor retention. TLX591-Tx+1TLX591-Tx ProstACT SELECT Study Published in Cancers JournalJul 21, 2026177Lu-DOTA-TLX591 Safety, Biodistribution and Dosimetry StudyNCT04786847
What the trial was built to test
The registered primary outcome measure was the number of participants with treatment-related adverse events by CTCAE v5.0 criteria, and the stated primary objectives were whole-body biodistribution, organ radiation dosimetry, and safety and tolerability. rPFS was a secondary objective. The design was open-label, single-arm, with no comparator, on 30 patients, which is well suited to characterizing dosing and tolerability but is not built to establish a controlled efficacy estimate. Principal investigator Nat Lenzo said the results "provide compelling evidence that the PSMA-PET imaging agent and TLX591-Tx are targeting the same disease sites, supporting the ongoing ProstACT Global trial for mCRPC". NCT04786847+1177Lu-DOTA-TLX591 Safety, Biodistribution and Dosimetry StudyNCT04786847TLX591-Tx ProstACT SELECT Study Published in Cancers JournalJul 21, 2026
Safety and the operational record
Telix described the safety profile as manageable and predictable in a population it called representative of a real-world setting, and the safety readout was characterized as consistent with the drug's known profile. Enrollment closed at 30 patients versus an original target of 50, a change registered alongside the status update to Completed in February 2024. The trial's primary completion date moved four times between 2021 and 2023 before the study closed, reflecting the operational path of a small, single-site-cluster early-phase dosimetry study rather than a signal specific to this efficacy figure. TLX591-Tx+1TLX591-Tx ProstACT SELECT Study Published in Cancers JournalJul 21, 2026177Lu-DOTA-TLX591 Safety, Biodistribution and Dosimetry StudyNCT04786847
The competitive field
PSMA-targeted therapy in prostate cancer is a crowded field: 111 active trials are studying the target in this indication, and 35% of Phase 1 PSMA-in-prostate-cancer trials have ended in termination. Novartis's Lutetium Lu-177 vipivotide tetraxetan, sold as Pluvicto, holds an existing FDA approval for PSMA-positive mCRPC after prior androgen-receptor pathway inhibitor therapy, and is running further Phase 3 and Phase 4 studies in the same population. Other direct comparators sharing PSMA and the radiopharmaceutical modality include AstraZeneca's AZD2265 and Novartis's AAA817, both in Phase 3 testing. Against that backdrop, TLX591-Tx's differentiated dosing schedule and its dosimetry profile of low salivary gland exposure and prolonged tumor retention are the features Telix is using to argue the drug clears a bar peers in the same class have not fully cleared on tolerability, though the bar that matters next is whether that translates into a survival or progression benefit under randomization. NCT04786847177Lu-DOTA-TLX591 Safety, Biodistribution and Dosimetry StudyNCT04786847
What comes next
Telix has already moved the program into the international Phase 3 ProstACT Global trial for mCRPC and frames this publication as scientific support for that ongoing registrational study. The company has not disclosed a specific timing window for the next data readout from ProstACT Global. TLX591-TxTLX591-Tx ProstACT SELECT Study Published in Cancers JournalJul 21, 2026
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