An experimental drug called VIR-5500 has produced striking early results in men with advanced prostate cancer.
Researchers reported tumour shrinkage and strong biomarker responses in a phase-one trial.
Prostate cancer remains the most common cancer in men in many countries.
About 1.5 million men receive the diagnosis worldwide each year.
Advanced cases often stop responding to standard treatments.
VIR-5500 uses an immunotherapy approach that activates the patient’s own immune system.
The engineered antibody links killer T-cells directly to tumour cells.
It becomes active mainly inside the tumour, which limits harmful inflammation.
This design may also allow less frequent dosing.
Fifty-eight men whose disease resisted other therapies received the drug.
Most experienced only mild side effects.
Among patients given the highest dose, 82% saw their PSA levels fall by at least half.
More than half recorded a drop of at least 90%.
Doctors also measured physical tumour changes.
Five of eleven men at the top dose showed clear tumour shrinkage.
One patient with liver metastases saw multiple lesions disappear after treatment cycles.
Researchers described the responses as unprecedented for a cancer long considered resistant to immunotherapy.
They are now planning larger trials to confirm safety and long-term benefit.
Independent experts called the findings highly encouraging but stressed the need for broader studies.
They highlighted the importance of testing across diverse patient groups.
Scientists hope this new class of therapy could extend survival and eventually lead to cures for advanced disease.
