Image caption Abiraterone has been shown to extend life for more than three months

A drug that can extend the life of men with advanced prostate cancer by more than three months has provisionally been rejected for NHS use.

Draft guidance from the health watchdog for England and Wales says the drug's benefits are not enough to justify the price the NHS has been asked to pay.

Cancer charities have been angered by the decision about abiraterone, one of the few drugs available to men in the final stages of prostate cancer.

A final decision is yet to be made.

Prostate cancer is the most common cancer to affect men in the UK.

The chief executive of the National Institute for Health and Clinical Excellence (NICE), Sir Andrew Dillon, said the drug was effective, and one of its key benefits was that it could be taken orally in the patient's own home.

"We are therefore disappointed not to be able to recommend it for use on the NHS, however it is an expensive drug," Sir Andrew added.

'Bitter blow'

Abiraterone costs just under £3,000 for one month's supply but has been offered at a undisclosed discounted price to the NHS.

Cancer charities have criticised the health regulator's decision.

"Quite simply, abiraterone prolongs the life of men with incurable prostate cancer. The draft decision is a bitter blow to thousands of men and their families and must be overturned," said Owen Sharp, chief executive of The Prostate Cancer Charity.

Case study: Ron McCoo, Blackpool Ron, 59, was diagnosed with prostate cancer in 2010. He has been using abiraterone for three months. His local health provider currently allows the drug to be used on an individual basis. He says it has changed his life. "I have my life back. I have a lot more energy and no pain. My quality of life is excellent. I wouldn't even know I have cancer now, it's that good. "I know it doesn't work for everybody but it certainly works for me. I would be devastated if it was no longer available on the NHS." Ron's wife Terri says: "We know NICE has to take a lot of things into consideration, but when you have a terminal illness an extra fourth months is very precious."

Prof Peter Johnson, Cancer Research UK's chief clinician, said: "Only one other drug is available on the NHS that has been shown to prolong survival but it has more severe side-effects than abiraterone and is effective in fewer men."

Cancer Research UK, which provided support in the development of the drug and could benefit from its royalties, said it believed that NICE might have overestimated the number of people who needed the drug.

It said that if the regulator rethought the criteria used to calculate the cost-effectiveness of the drug, there is a chance it could be made available under special arrangements for treating people at the end of their lives.

NICE said it had already used the appropriate methods in its review, and concluded that the number men who would need the drug was too large to consider such agreements.

Almost 500 men have successfully applied for abiraterone in the past nine months through the alternative route of the Cancer Drugs Fund in England, an initiative designed to increase access to drugs.

Until final guidelines are issued by the health regulator, decisions can continue to be made locally about the use of abiraterone.

Each year 37,000 men are diagnosed with prostate cancer, and more than 10,000 die from it.