Scientists said on Thursday a new drug had significantly reduced the size of skin cancer tumours in initial tests.
A team of US researchers said some melanoma patients in the trial saw a dramatic improvement in their condition and hailed the findings "a huge step forward."
"We are very excited about these results," said Dr Paul Chapman, involved in the research at the Memorial Sloan-Kettering Cancer Center in New York.
"We are seeing some pretty dramatic and rapid responses," he added.
The trial results, presented on Thursday at a major cancer conference in Berlin, showed some patients treated with the PLX4032 drug twice a day had seen their tumours shrink.
Thirty-one advanced melanoma sufferers with a cancer-causing gene mutation were involved in the trial.
Of 22 patients so far evaluated, tumours in 20 of them had reduced in size, according to Dr Chapman.
Melanoma is not the most common skin cancer but is one of the most difficult to treat successfully once it has started to spread, researchers said.
The drug in the trial works by blocking the activity of a mutation of the BRAF gene, which is thought to play a role in half of melanoma cancers.
Dr Chapman said the study was impressive as most of the patients, all of whom had the BRAF mutation, had already failed to respond to several previous treatments.
"A lot of these patients were pretty sick but many of them had a significant and rapid improvement in the way they function," he said.
"We've had patients come off oxygen and we've got several patients who have been able to come off narcotic pain medication soon after starting treatment."
The new treatment differs from standard chemotherapy, which aims to block rapid cancer cell division by attacking the machinery that causes this division.
In contrast, the PLX4032 drug directly attacks the genetic programme which causes the cells to divide uncontrollably.
But Dr Chapman cautioned that tests were at an early stage and scientists did not know how long the initial positive responses of the patients would last.
"I think this is a huge step forward; whether or not it will be sufficient by itself really remains to be seen," he said.
A second-phase trial involving about 90 patients is planned for the end of this year, as well as a third-phase trial of several hundred patients across the US, Europe and Australia.
The results came the same month a study by drug manufacturer Genentech, a subsidiary of Roche, showed evidence that a cancer pill reduced some skin cancer tumours in first-phase trials.