An experimental treatment has produced encouraging results for men with advanced prostate cancer.
Researchers reported tumour shrinkage in early trials of the drug VIR-5500.
Prostate cancer remains the most common cancer in men in many countries.
About 1.5 million new cases are diagnosed worldwide each year.
VIR-5500 uses immunotherapy to direct the immune system against cancer cells.
The engineered antibody links killer T-cells to tumour cells.
This allows the immune system to destroy cancers that normally evade detection.
Scientists designed the drug to activate mainly inside tumours.
This approach reduces harmful inflammation and may require fewer doses.
Fifty-eight men with treatment-resistant disease received the drug in a phase one trial.
Most participants experienced only mild side effects.
Researchers measured prostate-specific antigen levels to track response.
Among patients on the highest dose, 82% saw PSA fall by at least half.
More than half recorded reductions of at least 90%.
Some patients showed almost complete declines.
Five of eleven men with measurable tumours experienced visible shrinkage.
One patient saw multiple liver metastases disappear after several treatment cycles.
Scientists described the findings as unprecedented for a cancer considered resistant to immunotherapy.
They plan larger trials to confirm safety and long-term benefit.
Independent experts called the results highly promising but urged broader studies.
They stressed the need to include diverse patient groups.
Researchers hope the therapy will extend survival and improve quality of life.
They believe it could open a new treatment class for advanced prostate cancer.
