Ziggy Ojiegbe

A new experimental drug is raising hope for men with advanced prostate cancer, including those whose disease has spread and no longer responds to standard treatment.

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The medicine, known as VIR-5500, showed promising results in an early clinical trial involving 58 men with advanced prostate cancer.

The study was led by researchers at the Institute of Cancer Research and the Royal Marsden NHS Foundation Trust, with findings presented at a meeting of the American Society of Clinical Oncology in San Francisco.

Researchers reported that 45 percent of the men experienced tumor shrinkage. Among the 17 patients who received the highest dose, more than half saw their prostate-specific antigen, or PSA, levels drop by at least 90 percent. PSA is a blood marker commonly used to track prostate cancer. In the same high-dose group, 82 percent recorded a reduction in PSA levels of at least half.

VIR-5500 is a type of immunotherapy known as a T-cell engager. It works by attaching to the body’s immune T-cells and linking them to a protein found on prostate cancer cells, allowing the immune system to attack the disease directly. Immunotherapy has been successful in treating several other cancers, but it has not previously shown strong results in prostate cancer.

Researchers say this drug may be different because it uses a “cloaking” mechanism that keeps it inactive while circulating in the bloodstream and activates it only when it reaches the tumor. That design appears to reduce damage to healthy tissue. In the trial, 88 percent of patients experienced only mild side effects.

The study was funded by Vir Biotechnology.

Professor Johann de Bono, who led the research, said the drug will now move into larger trials to further test its safety and effectiveness. He said there is growing hope that treatments like VIR-5500 could improve outcomes for men with advanced prostate cancer and possibly increase the chances of a cure in the future.