VIR-5500 immunotherapy shows strong early responses in advanced prostate cancer
Feb 28th 2026
Early phase results show the tumor-activated immunotherapy VIR-5500 can shrink tumors and drive large PSA drops in many men with advanced prostate cancer while causing mostly mild side effects.
- VIR-5500 is an engineered T-cell engager designed to activate only inside tumors to limit systemic inflammation and stay in the bloodstream longer.
- A phase one trial gave VIR-5500 to 58 men with advanced prostate cancer who had stopped responding to other treatments.
- Eighty eight percent of participants experienced only very mild side effects.
- In 17 men at the highest dose, 14 (82%) had PSA fall by at least 50 percent, nine (53%) had at least 90 percent reduction and five (29%) had at least 99 percent reduction.
- Of 11 patients with measurable tumors at the highest dose, five showed tumor shrinkage including one case where 14 liver lesions resolved after six cycles.
- Results were presented at the American Society of Clinical Oncology genitourinary symposium, are not yet peer reviewed, and larger trials with more diverse patients are planned.