A watchdog U-turn could allow thousands of patients with the deadliest form of skin cancer to receive a pioneering drug that helps the immune system destroy tumours.
Ipilimumab, marketed as Yervoy, is one of the first of a new generation of immunotherapy drugs that have been hailed as a turning point in cancer treatment.
New final draft guidance from the NHS watchdog the National Institute for Health and Care Excellence (Nice) said ipilimumab should be available as a first treatment for patients with advanced and inoperable melanoma.
Nice was previously criticised for ruling the drug should only be offered to patients who had already undergone chemotherapy or were taking part in clinical trials.
Earlier this year, the guidance was changed to recommend "first line " use, but only in clinical trials.
Now, after fresh evidence of the drug's effectiveness, that restriction has been swept away.
If the latest draft guidance is approved - which is likely - patients will be eligible for ipilimumab even without first undergoing another form of treatment or taking part in a trial.
Professor Peter Johnson, chief clinician at the charity Cancer Research UK, said after the announcement: "This is good news for melanoma patients: it means that they have the chance to benefit from this new type of treatment without having to go through conventional chemotherapy first.
"Research is showing the huge promise of therapies such as ipilimumab, which manipulate the body's immune system to fight cancer.
"We're pleased that Nice and the manufacturer have been able to work together to make this drug available to more patients on the NHS."
A four-injection course of the treatment costs around £70,000 but the NHS has been given an undisclosed discount to make it more affordable.
Ipilimumab increases lifespan by an average of four months in melanoma patients whose cancer has spread.
But trial data suggests that one in five patients lives for at least three years after treatment.
Each year around 12,800 people in the UK are diagnosed with melanoma, and 2,200 die from the disease, which is notoriously hard to treat in its later stages.
It is estimated ipilimumab could help between 1,000 and 2,000 patients in the UK each year, many of them young.
Ipilimumab is a synthetic antibody that effectively takes a brake off the immune system, allowing the immune system's arsenal of T-cells to target tumours.
It is one of a number of new drugs that act on regulatory systems whose normal role is to keep the immune system under control.
Cancers such as melanoma are known to exploit these immune system "checkpoints" to shield themselves from the body's defences.
Ipilimumab suppresses a particular checkpoint "brake" called cytotoxic T-lymphocyte antigen 4 (CTLA-4).
Another drug, pembrolizumab, which targets a different checkpoint called PD-1, was recently in the headlines over the "miraculous" response of a trial patient with advanced melonama whose tumours appeared to melt away after treatment.
London TV engineer Warwick Steele, 64, had been given months to live after the cancer spread to his lungs.
Speaking about the case, consultant medical oncologist Dr David Chao, from Royal Hampstead NHS Trust in London, said: "This is one of several new drugs of this type being produced.
"What these early trials are showing is that they are fulfilling their promise ridiculously fast.
"Some of these results are really astonishing; almost jaw-dropping."
Researchers have tried combining different types of immune checkpoint drug together, with promising results.
In its final draft guidance, Nice said patients with advanced melonoma which is either inoperable or has spread to other parts of the body should be eligible for ipilimumab as a first-line treatment.
Nice chief executive Sir Andrew Dillon said: "We already recommend ipilimumab as a second-line treatment and so we are pleased to be able to propose extending that recommendation to first line treatment too.
"In previous draft guidance issued for consultation early this year, the committee recommended ipilimumab only be used by the NHS for patients in clinical trials.
"However, during the consultation, Bristol-Myers Squibb, the manufacturer of ipilimumab, submitted further information on how well the drug works.
"This information consisted of additional analysis of the existing data which demonstrated the degree to which the approved dose of ipilimumab can extend life when compared with current standard care in the NHS."
The draft guidance is still subject to appeal.
Final Nice guidance on ipilimumab is due to be issued on July 23.