A trial of a prostate cancer drug yielded unusual and exciting results when the drug being tested was found to be so effective that doctors concluded it would be unethical to deny it to all study participants.

After seeing results on the patients in the test group, researchers testing Radium-223 Chloride -- known as Alpharadin TM -- at London's Royal Marsden Hospital halted the drug trial so that the placebo group could also have access to the drug. Initially, only 461 cancer sufferers were given the drug, but after the results were observed the drug was given to all 922 patients in the trial.

It would have been unethical not to offer the active treatment to those taking placebo,  Dr. Chris Parker, lead researcher on the project, said at the 2011 European Multidisciplinary Cancer Congress on Saturday.

The drug was primarily being tested for its efficacy in treating bone mestatases, which occurs in many advanced cancers. Researchers chose to test it on patients with prostate cancer because 90% of all men with advanced prostate cancer will experience bone mestaseses.  All 922 prostate cancer patients in the trial had bone metastases and were resistant to hormone treatment.

Compared to chemotherapy, which affects all the tissues of the body, radium-223 is highly targeted to the bone metastases, and it has a completely different safety profile, said Dr.  Parker.

I have no doubt that there will be further trials looking at a combination of radium-223 with other drugs that are currently used in prostate cancer, and that there will also be studies using radium earlier in the disease. In particular, our research was restricted to those men who were not going to receive chemotherapy for prostate cancer. It would be interesting to use radium-223 chloride before chemotherapy, since it might be even more effective in that setting.

Additionally, the drug could be used in many other types of cancers which metastasise to bone, regardless of the primary site. We believe that our trial may have paved the way for improvements in survival for very many cancer patients, Dr. Parker continued.

The patients in the trial experienced minimal side effects. The death rate among the initial test group was 30 per cent lower in the group taking radium-223.

This appears to be an important study using a highly targeted form of radiation to treat prostate cancer that has spread to the bones, Prof. Gillies McKenna, Cancer Research UK's radiotherapy expert, told the Telegraph.

This research looks very promising and could be an important addition to approaches available to treat secondary tumours - and should be investigated further.

The researchers will submit the data for regulatory approval.

I would hope that the authorities will approve radium-223 as a treatment for bone metastases in advanced prostate cancer soon, Dr. Parker said. This is a common cancer - the second commonest cancer killer in men in the UK - and so it's a big disease burden. We urgently need effective treatment for it.