Researchers have reported encouraging early results for a new prostate cancer treatment.
The experimental drug VIR-5500 shrank tumours in several men with advanced disease.
Prostate cancer affects about 1.5 million men worldwide each year.
Immunotherapy has transformed other cancers but rarely works in this one.
Scientists now believe this approach may finally change that.
VIR-5500 is an engineered antibody that links killer T-cells to tumour cells.
It activates mainly inside the tumour, which limits harmful inflammation.
The design also allows the drug to remain longer in the bloodstream.
Fifty-eight men whose cancer resisted standard treatments joined the phase-one trial.
Most experienced only mild side effects.
At the highest dose, PSA levels fell by at least half in 82% of patients.
More than half saw reductions of 90% or greater.
Five men showed clear tumour shrinkage on scans.
One patient with cancer spread to the liver saw fourteen lesions disappear.
Researchers called the findings unprecedented for an immune-resistant disease.
The results still require peer review and larger trials.
Experts say the therapy could open a new drug class for prostate cancer.
They also stress the need for studies in diverse patient groups.
With thousands of deaths each year in the UK alone,
scientists hope this treatment will extend and improve lives.
