'Stunning' New Prostate Cancer Drug Shows Remarkable Results in UK-Led Trial
A new immunotherapy drug called VIR-5500 has produced what researchers are describing as "stunning" and "unprecedented" results in a Phase 1 clinical trial for men with advanced prostate cancer, with the trial led by scientists at the Institute of Cancer Research in London.
The drug, which uses a novel "cloaking device" mechanism to target tumour cells while minimising side effects, showed significant reductions in cancer markers and tumour shrinkage in a substantial proportion of patients who had exhausted all other treatment options. The findings were presented at the American Society of Clinical Oncology Genitourinary Cancers Symposium in February 2026.
Key Developments
In the highest dose cohorts of the trial, 82% of evaluable patients saw their prostate-specific antigen (PSA) levels fall by at least half, while 53% experienced a PSA reduction of at least 90%. Among patients whose tumours were measurable, 45% showed tumour shrinkage.
In one remarkable case, a 63-year-old man whose cancer had spread to his liver saw all 14 cancerous liver lesions completely resolve after six treatment cycles. Another patient, aged 70, experienced complete resolution of small tumours outside the prostate.
The trial involved 58 men across eight global sites, led by Professor Johann de Bono of the Institute of Cancer Research and the Royal Marsden NHS Foundation Trust. Professor de Bono described the results as "unprecedented" for a disease previously considered resistant to immunotherapy.
Background
Prostate cancer is the most common cancer among men in the UK, with over 12,000 men dying from the disease annually. Advanced prostate cancer that has stopped responding to other treatments has historically been extremely difficult to treat, making new therapeutic options critically important for patients and their families.
VIR-5500 works as a T-cell engager — an engineered antibody that brings the body's killer T-cells into contact with tumour cells. Its unique "PRO-XTEN dual-masked" technology keeps the drug inactive until it reaches the tumour microenvironment, where it is activated by tumour-specific enzymes. This targeted approach minimises the severe inflammatory responses that have hampered previous T-cell engager drugs.
Why It Matters
The results represent a potential breakthrough for one of the UK's most significant cancer burdens. If larger trials confirm the Phase 1 findings, VIR-5500 could offer a new treatment pathway for thousands of British men each year whose cancer has stopped responding to existing therapies.
What's Next
Vir Biotechnology plans to initiate expanded dose cohorts in the second quarter of 2026, with pivotal Phase 3 trials anticipated to begin in 2027. Full details of the trial results are available at The Independent.
