New drug shows 'stunning' results in advanced prostate cancer

VIR-5500, a T-cell engager drug, shrank tumors in men with treatment-resistant prostate cancer.

Mar. 13, 2026 at 7:00am by Ben Kaplan

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In an early-stage clinical trial, 58 men with advanced prostate cancer who had stopped responding to existing treatments were given VIR-5500, an engineered antibody developed by Vir Biotechnology. At the highest dose, 82% of patients saw their PSA levels drop by at least half, with 53% seeing a 90% or greater decrease. Five of 11 patients with measurable tumors showed tumor shrinkage, including one case where 14 liver lesions completely resolved.

Why it matters

Prostate cancer has largely been resistant to immunotherapy, which has transformed treatment for other cancer types. These early results suggest VIR-5500 could open up a new class of drugs for prostate cancer, offering hope for men with advanced, treatment-resistant disease.

The details

VIR-5500 is a T-cell engager, a type of drug that introduces the immune system's killer T-cells to tumor cells that are trying to evade them, allowing the T-cells to destroy them. Unlike other T-cell engagers, VIR-5500 is designed to only activate inside the tumor, which keeps side effects low and allows the drug to stay in the bloodstream longer.

  • The results were presented at the American Society of Clinical Oncology genitourinary cancers symposium in San Francisco in March 2026.

The players

VIR-5500

An engineered antibody developed by Vir Biotechnology that is a T-cell engager drug.

Prof. Johann de Bono

The researcher who led the study on VIR-5500 and is from the Institute of Cancer Research and the Royal Marsden NHS Foundation Trust.

Charlotte Bevan

A professor of cancer biology at Imperial College London who was not involved in the research but called the potential advance "very exciting".

Simon Grieveson

The assistant director of research at Prostate Cancer UK, who said these early results are "extremely promising" and looked forward to seeing the treatment tested in larger trials.

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What they’re saying

“We do need more data but the results are stunning. We believe that such treatments may in the long term lead to cures.”

— Prof. Johann de Bono (The Optimist Daily)

“These early results are extremely promising, with a number of men on the study responding positively to the treatment with minimal side effects. I look forward to seeing this now tested in larger trials, with the hope that this treatment will offer men more valuable time with their loved ones.”

— Simon Grieveson, Assistant Director of Research, Prostate Cancer UK (The Optimist Daily)

What’s next

Further clinical trials are now being planned to test VIR-5500 in a larger patient population.

The takeaway

These early results on VIR-5500 offer hope for a new class of immunotherapy drugs that could transform treatment for men with advanced, treatment-resistant prostate cancer, a cancer type that has long been resistant to such approaches.