A trial has found a combination of two drugs designed to boost the body's natural defences can wipe out the most deadly form of skin cancer, even when the disease is advanced.
Of 95 patients given the treatment, more than 60% were still alive after two years.
More than a fifth - 22% - had no detectable tumours remaining.
A total of 142 patients were randomly allocated either to receive two drugs, nivolumab and ipilimumab, or ipilimumab alone.
The therapies, consisting of lab-made antibodies, are designed to overcome the ability of some cancers to evade the immune system.
Findings from a Phase II US-led trial testing the effectiveness of the drug combination were presented at the annual meeting of the American Association for Cancer Research in New Orleans.
British expert Dr James Larkin, consultant medical oncologist at the Royal Marsden Hospital, has treated patients with the drugs as part of another on-going trial.
Dr Larkin said: "Both nivolumab and ipilimumab have changed survival expectations in advanced melanoma over the last few years and these latest data show us that combining these two immunotherapies is an effective two-pronged attack against the cancer.
"The overall survival rates observed using the regimen of nivolumab plus ipilimumab are very promising and provide further hope for patients and their families affected by this disease."
Melanoma is at the forefront of new immunotherapy approaches to cancer treatment.
The immune system is constantly fighting a battle with cancer, and usually wins. But sometimes it fails, due to cancers exploiting mechanisms designed to prevent a too-strong immune response harming the body's own tissues.
The antibody drugs, known as "checkpoint inhibitors", interrupt two different signalling pathways to take the brakes off the immune system.
Each blocks a separate receptor "switch" on immune system T-cells that weakens the immune response and can be activated by molecules released by tumours. Ipilimumab targets a receptor called CTLA-4 while the newer drug nivolumab homes in on the PD-1 receptor.
Patients taking part in the trial had two common forms of melanoma, one with a "normal" version of the BRAF gene and the other with a mutated version.
A total of 69% of patients from the normal or "wild-type" BRAF group treated with the combination therapy were still alive after two years.
For the whole population of combination therapy patients, two-year survival was achieved by 64%.
Trial co-leader Dr Stephen Hodi, director of the Melanoma Centre at Dana-Farber Cancer Institute in the US, said: "These data contribute to our growing understanding of this aggressive cancer and are promising news for advanced melanoma patients.
"In particular, we are seeing further data that evaluate the potential survival benefit of the nivolumab and ipilimumab combination."
Checkpoint inhibitors can have side effects linked to the way they impact on the immune system which may cause skin, gastro-intestinal, liver and hormonal problems.
In the trial, the adverse effects associated with the combination treatment included rash, itching, diarrhoea, gut inflammation and raised levels of a marker of liver damage.