Melanoma can start in a mole or in normal skin
Scientists say they have developed a drug that can treat the most deadly form of skin cancer in its most advanced, incurable stages.
Malignant melanoma is the most rapidly increasing cancer in the UK, largely due to sun exposure.
An experimental drug PLX4032 (R7204) could help many patients with incurable disease live longer with the disease in check, early trial results suggest.
Roche and Plexxikon presented the work at a renowned US cancer meeting.
Experts welcomed the findings and urged people to take care when out in the sun this summer, which is tipped to be hot.
PLX4032 works by seeking out and destroying tumour cells carrying the BRAF mutation implicated in 60% malignant melanomas.
This could not only help to shrink the skin cancer, but also delay its spread.
Currently, only a small proportion of people - less than 5% - live more than two years if their cancer has spread around the body.
In a phase I study involving 16 patients with BRAF-positive melanoma, over half saw the extent of their cancer reduce by at least 30%.
Patients treated with PLX4032 lived for a median of six months without their disease getting worse and more than half experienced significant shrinkage of their tumours.
This included patients where the cancer had spread to the liver, lung and bone.
Roche and its partner Plexxikon told delegates at the American Society of Clinical Oncology meeting in Florida that they now plan larger trials to further test the drug's safety and check things like what dose is best.
They also hope to make a diagnostic test to easily spot which patients have BRAF-positive melanoma.
In the UK, more than 10,400 people are diagnosed with malignant melanoma each year.
The most serious form of skin cancer
Sun exposure is the main - and most preventable - risk factor, causing genetic damage to the skin
Around one third of melanomas develop from normal moles
The rest develop on areas of previously normal skin
Warning signs include:
Two halves of a mole do not look the same
The edges of the mole are irregular, blurred or jagged
Colour is uneven, with more than one shade
Mole is wider than 6mm
Treatments for advanced melanoma, such as chemotherapy, can lead to an improvement in symptoms and quality of life but do not greatly extend life.
And some people will get the side-effects without many of the benefits.
For these reasons scientists are looking for new therapies.
Others are researching vaccines to treat advanced melanoma by encouraging the body's own immune system to destroy the cancer cells.
Dr Jodie Moffat of Cancer Research UK said: "While these results are interesting, they need to be followed up in much larger studies before we know if this is a suitable new treatment for people with advanced melanoma.
"Melanoma is difficult to treat when it is at an advanced stage so it's crucial to find new treatments to help beat the disease.
"When melanoma is diagnosed early, treatment is often simpler and more likely to be effective. If you notice a change in the size, shape or colour of a mole or other patch of skin, make sure you get it checked out by your doctor without delay.
"Excessive exposure to ultraviolet radiation, from the sun or from sunbeds, is the leading cause of skin cancer.
"With this year's summer expected to be hotter than the last, it's important that we don't let sunburn catch us out. Whether at home or abroad, use shade, clothing and sunscreen of SPF 15 or higher to protect your skin."