Prof William Kelly speaks to ecancer about findings from a first-in-human study evaluating the feasibility and safety of administering xaluritamig with a shortened monitoring period in patients with previously treated metastatic castration-resistant prostate cancer (mCRPC).

Xaluritamig is a STEAP1-targeting CD3 T-cell engager designed to direct T cells against prostate cancer cells. The study evaluated 20 patients receiving xaluritamig with 4–6 hours of monitoring for all step-up doses, including the first treatment, alongside dexamethasone premedication and patient and caregiver education on recognising cytokine release syndrome (CRS).

Prof Kelly says grade 3 treatment-emergent adverse events occurred in 90% of patients, primarily myalgia. CRS occurred in 60% of patients and was limited to grade 1 or 2, with no grade 3 or higher CRS events reported. 

He highlights that preliminary antitumour activity was consistent with previous findings, with confirmed PSA reductions of at least 50% in 61% of evaluable patients and a confirmed objective response rate of 50% among the six patients evaluable for this outcome.

These results support the feasibility of shorter monitoring with xaluritamig and provide a foundation for the ongoing phase III XALience study investigating its use with abiraterone in a fully outpatient setting.

Prof Kelly discusses the clinical significance of reducing monitoring to 4–6 hours and how this could affect the treatment experience for patients with mCRPC. He also explores the management of CRS and other immune-related toxicities in an outpatient setting, how clinicians should interpret the preliminary efficacy findings alongside the safety data, and what further evidence is needed.

Finally, he considers the key questions the phase III XALience study must address before this approach can be adopted more widely.