New Immunotherapy Drug Shows Promise for Advanced Prostate Cancer

VIR-5500 shrinks tumors and reduces key cancer biomarker in clinical trial

Published on Feb. 28, 2026

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A new immunotherapy drug called VIR-5500 has demonstrated promising results in a phase one clinical trial for men with advanced prostate cancer. The drug was able to shrink tumors in some patients and significantly reduce levels of prostate-specific antigen (PSA), a key cancer biomarker, with mostly mild side effects.

Why it matters

Prostate cancer is the most common cancer among men worldwide, and advanced cases that stop responding to other treatments have limited options. If further trials confirm these early findings, VIR-5500 could represent a major breakthrough in treating this deadly disease.

The details

The trial, led by researchers at the Institute of Cancer Research, London and The Royal Marsden NHS Foundation Trust, involved 58 men whose prostate cancer had stopped responding to other treatments. Results showed that for 17 men receiving the highest dose, 14 (82%) saw their PSA levels fall by at least half, 9 (53%) experienced a reduction of at least 90%, and 5 (29%) saw a fall of at least 99%. Among 11 patients with measurable tumors, 5 showed evidence of shrinkage, and in one case, a 63-year-old man with liver metastases experienced complete resolution of 14 lesions.

  • The clinical trial results were presented on February 28, 2026 at the American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium in San Francisco.

The players

Professor Johann de Bono

Lead researcher of the clinical trial, from the Institute of Cancer Research, London and The Royal Marsden NHS Foundation Trust.

Vir Biotechnology

The company that funded the phase one clinical trial of VIR-5500.

Simon Grieveson

Assistant director of research at Prostate Cancer UK, who called the results "extremely promising".

Charlotte Bevan

Professor of cancer biology at Imperial College London, who cautioned that future studies should include patients of diverse ethnicities.

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What they’re saying

“We believe that such treatments may in the long term lead to cures.”

— Professor Johann de Bono

“We urgently need new and innovative ways to treat the disease.”

— Simon Grieveson, Assistant director of research at Prostate Cancer UK

“Future studies should include patients of diverse ethnicities, given disparities in prostate cancer outcomes.”

— Charlotte Bevan, Professor of cancer biology at Imperial College London

What’s next

Researchers are now planning further clinical trials to confirm these early findings of VIR-5500's efficacy in treating advanced prostate cancer.

The takeaway

This new immunotherapy drug represents a potentially groundbreaking advancement in the treatment of a disease that has historically been resistant to such therapies. If future trials are successful, VIR-5500 could offer new hope for men with advanced prostate cancer who have exhausted other treatment options.