Vir Biotechnology to present tolerability and anti-tumour signals for VIR-5500 in prostate cancer at ASCO GU 2026
Vir Biotechnology announced new data from the ongoing Phase 1 clinical trial of VIR-5500, a prostate-specific membrane antigen (PSMA)-targeting, Pro -xten dual-masked T-cell engager (TCE) being evaluated in patients with advanced metastatic castration-resistant prostate cancer (mCRPC) who have progressed after multiple lines of therapy (NCT05997615). These data suggest that VIR-5500 monotherapy is well tolerated and exhibits promising anti-tumor activity. Data will be presented in an oral presentation at the 2026 American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium on February 26 in San Francisco, CA (Oral Abstract #17).
Data across all patients receiving VIR-5500 monotherapy in the Phase 1 trial (n=58) show that VIR‑5500 was generally well tolerated with no dose‑limiting toxicities (DLTs) observed to date. Grade ≥3 treatment‑related adverse events occurred in 12% (7/58) of patients and were manageable. Limited cytokine release syndrome (CRS) was observed in 50% (29/58) of patients, with events generally restricted to Grade 1 (fever only). Prophylactic steroids were not required and were only explored in a small cohort of three patients. Enrolled patients were heavily pre-treated (median of four prior lines) and a substantial proportion presented with high tumor burden, including nearly one half with visceral metastases.
Dose‑dependent activity was observed across the entire treatment group as measured by both prostate-specific antigen (PSA) declines and radiographic responses. Efficacy data were reported in the highest dose cohorts (≥3,000 µg/kg Q3W; n=22/58) as of the January 9, 2026 data cut-off. In these cohorts, PSA50 declines occurred in 82% (14/17) and PSA90 declines in 53% (9/17) of PSA-evaluable patients. Among RECIST (Response Evaluation Criteria in Solid Tumors)‑evaluable patients, objective responses were seen in 45% (5/11). Of the five responders, four achieved confirmed responses with one patient pending confirmation. Reductions on PSMA‑PET (positron emission tomography) affirm PSA declines and radiographic responses, with tumor shrinkage observed across multiple lesions, including visceral metastases. These findings support proof‑of‑concept and further evaluation in expansion cohorts.
Vir Biotechnology has concluded QW and Q3W monotherapy dose-escalation in late-line mCRPC and has defined a preliminary go-forward dose and regimen recommendation for expansion. In parallel, dose-escalation of VIR-5500 in combination with enzalutamide continues in early-line mCRPC patients. The Company anticipates initiating monotherapy dose-expansion cohorts in late-line mCRPC and combination dose-expansion cohorts in both early-line mCRPC and metastatic hormone-sensitive prostate cancer (mHSPC) in the second quarter of 2026 followed by pivotal Phase 3 trials in 2027.
