The results of a clinical trial into the effectiveness of a new immunotherapy drug for a deadly form of skin cancer are set to be presented at an upcoming conference, with researchers hailing the study as “a step forward” in the quest to overcome the affliction.

Melanoma is a condition whereby the skin’s pigment-producing cells – called melanocytes – become cancerous. Often spreading to other parts of the body, the disease typically has a very low survival rate. According to Caroline Robert, who led the study, prior to 2011 the average melanoma sufferer lived for less than one year.

The difficulty in treating the disease owes to the fact that cancer is simply a mass of malfunctioning body cells, rather than an external pathogen. Because the body’s immune system contains a number of mechanisms that prevent it from destroying its own cells – ensuring it only targets alien invaders – it does not attack these cancerous cells.

For example, a protein called programmed cell death protein 1 (PD-1) is found on the surface of white blood cells, and serves to keep them in check by preventing them from attacking other body cells. However, by deactivating this safety feature, researchers suspect it may be possible to temporarily recruit the immune system to destroy cancerous cells.

To achieve this, they experimented with a compound called pembrolizumab, which inhibits the activity of PD-1. They gave 655 melanoma patients the drug during the trial, 40 percent of whom remained alive three years later.

The research, which will be presented at the American Society of Clinical Oncology's annual conference, has been met with a great deal of excitement, and represents something of a breakthrough in the search for a cure for melanoma. For instance, the average survival time for patients who received pembrolizumab was 23.8 months – considerably longer than sufferers were previously expected to survive.

Daniel Hayes, the president-elect of the American Society of Clinical Oncology, told the BBC that melanoma “has been a bad disease, it's hard to treat, it's a sneaky disease and the mortality rates have been enormous so to see 40 percent of patients alive at three years is really a step forward.”

“We're even wondering if we could use the word cure here, but it's going to take longer follow up,” he added.