Researchers have reported encouraging early results for a new prostate cancer treatment.
The experimental drug VIR-5500 shrank tumours in some men with advanced disease.
Prostate cancer affects about 1.5 million men worldwide each year.
Immunotherapy has transformed other cancers but rarely benefits this disease.
Scientists now believe this approach may finally work in prostate cancer.
VIR-5500 is an engineered antibody that redirects killer T-cells toward tumour cells.
The drug activates mainly inside the tumour, which limits harmful inflammation.
It can also remain longer in the bloodstream and may require fewer doses.
The phase 1 trial treated 58 men whose cancer resisted standard therapies.
Most participants experienced only mild side effects.
Researchers measured changes in prostate-specific antigen levels to assess response.
At the highest dose, 82% of patients saw PSA levels fall by at least half.
More than half recorded reductions of 90% or greater.
Nearly a third showed a drop of at least 99%.
Among patients with measurable tumours, almost half showed visible shrinkage.
One man with liver metastases saw multiple lesions disappear completely.
Scientists described the findings as unprecedented for an immune-resistant cancer.
They are planning larger trials to confirm safety and effectiveness.
Independent experts called the results exciting but urged broader studies.
They want trials that include diverse patient groups and long-term outcomes.
Researchers hope this strategy could extend survival and eventually lead to cures.
