A pair of drugs that uses the immune system to attack cancer cells shrunk tumours in nearly 60 per cent of people with advanced melanoma according to a recent study in the U.K. — though questions about survival, side-effects and cost remain.

Melanoma is the most serious form of skin cancer, with an estimated 6,800 new cases of malignancy expected to be diagnosed with year, according to the Canadian Cancer Society.

Melanoma is the most serious form of skin cancer. (Joe Raedle/Getty)

Normally the immune system has brakes that stop it from attacking our own cells. But cancerous cells are able to evade the immune system by keeping those brakes, or "checkpoints," on permanently.

Immunotherapy aims to get the immune system to recognize and target cancerous cells.

"What these drugs do is they take off those switches, they undo those checkpoints as they're called, so they're checkpoint inhibitors. So therefore they allow the immune system to recognize the cancer cells as abnormal and then reject them," said Mark Harries, a consultant medical oncologist at Guy's and St Thomas Hospital in London, U.K., who was not involved in the study.

The British-led randomized trial involved 945 people with advanced melanoma who were randomly assigned to ipilimumab and nivolumab to see if the combination stopped the skin cancer from worsening. It did in 58 per cent of the cases, Dr. Jedd Wolchock of the Memorial Sloan Kettering Cancer Center in New York and his team reported in The New England Journal of Medicine.

The tumours were stable or shrank for an average of 11.5 months, researchers found. In comparison, the same study found tumours shrank or were stable for an average of 6.9 months among those who received nivolumab alone, and for 2.9 months in the ipilimumab-only group.

The study's authors said it will be "interesting to determine whether the efficacy results reported here will be reflected in an overall survival benefit."

Toxic effects

Serious drug-related side-effects such as toxic effects on the liver were reported by more than half of those in the combination group (55 per cent). About 36 per cent of patients in this group had to stop the therapy.

"Combining these treatments also increases the likelihood of potentially quite severe side-effects," cautioned Dr. Alan Worsley, Cancer Research UK's senior science information office. "Identifying which patients are most likely to benefit will be key to bringing our best weapons to bear against the disease."

The research was also presented on Sunday at the American Society of Clinical Oncology's annual meeting in Chicago.

Dr. Leonard Saltz, also with the Memorial Sloan Kettering Cancer Center, who was not involved in the study, told the meeting the current prices of the two drugs push the cost of the regimen into the hundreds of thousands of dollars.

Both drugs were developed by Bristol-Myers Squibb, which funded the clinical trial.