Four-in-10 patients who had a deadly skin cancer were still alive after three years after being given the drug.
What's even more promising is that 15 per cent of those that were given the drug showed no signs of cancer at all.
The drug, pembrolizumab, is part of a new wave of immunotherapies which essentially tweaks the way our immune system works.
While the human body is incredibly capable of fighting infections, it has a lot of safeguards built in to stop it attacking human tissues.
Unfortunately that's precisely what cancer is, which means that the disease can more often than not bypass our immune system.
What pembrolizumab does then is remove those safeguards from our immune system and essentially give the body's immune system a new target, in this case skin cancer cells.
Skin cancer has a reputation of being one of the most aggressive forms of the disease - mortality rates are often incredibly high.
President-elect of the American Society of Clinical Oncology Dr Daniel Hayes explained the importance of this drug: "This 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% 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."
Thanks to some very early and clear successes with the drug the findings are already being put into action with the NHS approving pembrolizumab for patients with melanoma.