A new prostate cancer drug trial has been so successful doctors have decided to stop it early.
Medics at London's Royal Marsden Hospital were testing a powerful alpha radiation drug on 461 people while another group of the same number were being treated with a dummy drug.
Patients taking the new drug experienced less pain, side effects and lived longer.
Researchers were so astounded with the results they decided to stop the trial and started treating all 922 patients taking part in the study because they said it would be unethical not to.
Radiation has long been used to treat tumours and damages the genetic code inside cancer cells.
However, alpha particles are the most powerful radiation and consist of helium nuclei, which are bigger and strong than beta radiation - a stream of electrons.
Dr Chris Parker, who is the lead researcher on the study, said it was a significant step forward for cancer research.
'It's more damaging. It takes one, two three hits to kill a cancer cell compared with thousands of hits for beta particles,' he told the BBC.
Dr Parker also said that less damage was done to surrounding cells and added the radiation only targeted only the cancer.
Many patients with advanced prostate cancer will have little chance of survival because the tumour usually spreads to the bone.
The study originally looked at patients with these secondary cancers and used the radium-223 chloride drug, which acts like calcium and sticks to the bone.
Half were given the new drug and the others were treated with chemotherapy and a dummy pill which had no effect.
The death rate was 30 per cent lower in the group taking radium-223 and patients survived for 14 months on average compared with the other group which survived 11 months on average.
Dr Parker said the decision was then made to abandon the trial and treat everyone taking part because 'it would have been unethical not to offer the active treatment to those taking placebo'.
Researchers said the new treatment was safe and added that those taking it suffered less side-affects than those taking the dummy medicine.
Cancer Research UK has said the research is promising and could be an important addition to treating patients with secondary tumours.
Prof Gillies McKenna, the charity's radiotherapy expert and director of the Gray Institute for Radiation Oncology and Biology, said: 'This appears to be an important study using a highly targeted form of radiation to treat prostate cancer that has spread to the bones.'
