Researchers praise ‘stunning’ results of new prostate cancer treatment

February 28, 2026

TL;DR

A new immunotherapy drug, VIR-5500, shows promise in early trials for advanced prostate cancer.
VIR-5500 is a T-cell engager that targets cancer cells and activates the body's immune system.
The drug is designed to activate within the tumor, minimizing side effects and potentially requiring fewer doses.
In a phase one trial, 88% of patients experienced only very mild side effects.
Among patients given the highest dose, 82% saw their PSA levels fall by at least half, and 29% experienced a fall of at least 99%.
Tumor shrinkage was observed in 5 out of 11 patients with measurable tumors at the highest dose.
One patient with advanced prostate cancer that had spread to the liver experienced complete resolution of 14 cancerous liver lesions.
Experts describe the results as 'stunning' and 'unprecedented' for prostate cancer, a disease often resistant to immunotherapy.
Further clinical trials are planned to validate these findings.

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