A clinical trial has also shown the drug Yervoy can help prolong life in patients who have already tried other treatments.
The National Institute for Health and Clinical Excellence (Nice) has yet to decide whether the treatment, which is also known as ipilimumab, will be available on the NHS.
But some 15 patients in Wales have already been treated with the drug as part of the phase III clinical trial.
One of those patients, a 76-year-old man from Aberdare, underwent a course of treatment after being diagnosed with cancer last year.
A year after he had the last dose, the disease has stabilised.
The man, who has asked not to be named, said: “The first lot of ‘normal’ chemotherapy didn’t work and I was asked whether I’d be prepared to go on this trial. I said yes because I had nothing to lose.
“Having the treatment was no trouble at all, but after the first session, just as I was about to start the second, I developed a rash, which was the worst part.
“It had to be treated with different creams, but I kept up with the treatment because it was working and that’s the main thing.
“You have to put up with some things – I put up with the rash but the treatment helped me.”
The drug works by stimulating the body’s own immune system to fight cancer.
In clinical trials, 46% of patients who received it were still alive after one year, compared to 25% of those in the comparator group.
The median survival was 10.1 months among those patients taking the drug, compared to 6.4 months in the other group – the median overall survival for patients with advanced skin cancer is six to nine months.
Dr Satish Kumar, a medical oncologist at Velindre Cancer Centre, said: “This represents hope for our patients as previously there wasn’t really anything for this set of patients with advanced melanoma – there weren’t any drugs that could prolong life.
“This drug has been shown to prolong life in these patients.”
Dr Paul Lorigan, a senior lecturer in medical oncology at the Christie NHS Foundation Trust, in Manchester, added: “The authorisation of ipilimumab represents a real advance in the treatment of patients with advanced melanoma, as this is the first treatment for 40 years to extend patients’ life expectancy.
“After years of no progress in the treatment of this terrible illness, we have now made a stride forward.”
And Richard Clifford, trustee of the charity SKCIN, which raises awareness of skin cancer, said: “A diagnosis of metastatic melanoma is devastating news for anyone to receive.
“We have long awaited the arrival of new effective treatment options, which makes today’s news very welcome.”
The latest figures show the number of people being diagnosed with malignant melanoma is increasing in Wales, in line with the rest of the UK.
More young people are also developing the aggressive disease, largely as a result of the growth in foreign holidays and the popularity of sunbeds.
Cases in men rose 48% between 2004 and 2008, to more than 300 a year and there was a 19% rise (to 295 cases) in the number of women diagnosed with malignant melanoma in the same period.
New skin cancer drug licensed for use in the UK