A pill for advanced skin cancer that targets patients with particular genetic make-up had dramatic results, scientists revealed.
In 80 per cent of those treated, tumours were significantly reduced in size.
The patients were suffering from malignant melanoma, the most dangerous form of skin cancer, which started to spread.
Most had mutations in the BRAF gene which occur in 40 per cent to 60 per cent of patients with the disease.
The drug, PLX4032, inhibits faulty BRAF and prevents it stimulating the cancer.
Lead researcher Dr Paul Chapman, from the Memorial Sloan-Kettering Cancer Centre in New York, said: "We have seen many tumours shrink rapidly, and in some patients, quality of life improved dramatically.
"This is the beginning of personalised medicine in melanoma."
A total of 87 patients took part in the Phase II study and were treated with increasing doses of PLX4032.
Two complete and 24 partial responses were seen among the 32 patients treated with a full dose of the drug.
Tumour shrinkage was seen at all cancer sites, including the liver, small bowel and bone.
Currently 16 individuals are still taking part in the trial, whose findings are published in the New England Journal of Medicine.
Dr Chapman is now heading a larger Phase III patient study.
He said: "We have never seen an 80 per cent response rate in melanoma, or in any other solid tumour for that matter, so this is remarkable.
"The tumour responses induced by PLX4032 are not always long-lasting though, and we don't know if treatment really improves overall survival of melanoma patients. That is what we are trying to find out in the ongoing Phase III trial.
"In future, we hope to combine PLX4032 with other anti-melanoma drugs currently being developed."
Around 1,500 people die from malignant melanoma each year in England and Wales. The disease is triggered by over-exposure to the sun.
If allowed to reach an advanced stage, the cancer is deadly and the chances of a cure low.
Bevis Man, from the British Skin Foundation, said: "This news is certainly cause for optimism in the fight against skin cancer. However, it's worth noting that this is by no means a green light for the general public to go out and put themselves at risk of developing skin cancer by wrongly believing there is now a simple cure.
"The fact is that malignant melanoma kills close to 2,000 people every year in the UK. For the time being at least the focus needs to remain firmly on preventing skin cancers from occurring in the first place, so those all important sun safety messages remain a vital key to this."Reuse content