Researchers have reported strong early results for the experimental drug VIR-5500.
The treatment shrank tumours in men with advanced prostate cancer.
Prostate cancer remains the most common cancer in men in many countries.
About 1.5 million new cases appear worldwide each year.
VIR-5500 uses immunotherapy to direct the immune system against cancer.
The engineered antibody links killer T-cells to tumour cells.
It activates mainly inside the tumour, which limits harmful inflammation.
This design may also reduce the number of required doses.
Scientists tested the drug in 58 men who no longer responded to standard treatments.
Most participants experienced only mild side effects.
Researchers measured prostate-specific antigen levels to assess response.
Among patients on the highest dose, most showed major PSA reductions.
Several recorded drops of more than ninety percent.
Some patients also showed clear tumour shrinkage.
One man with cancer spread to the liver saw multiple lesions disappear.
Experts described the findings as unprecedented for this disease.
Prostate cancer has long resisted immunotherapy approaches.
The results still come from an early-stage trial.
Larger studies must confirm long-term safety and effectiveness.
Specialists say the treatment could open a new class of therapies.
They also stress the need for diverse patient groups in future trials.
Researchers now plan expanded studies to test the drug further.
They hope the approach will extend survival and improve quality of life.
