A drug, already used to treat melanoma, has successfully saved the lives of terminally ill lung cancer patients who took part in a global medical trial.

Patients with terminal lung cancer have been given a second chance at life after they were successfully treated with a drug doctors are hailing as a game-changer in the way the deadly disease is treated.

Pembrolizumab, commonly known as Keytruda, is a form of immunotherapy and is already listed on the PBS for melanoma patients.

It essentially works by targeting a "cunning"' protein marker found on cancer cells, known as PD-L1, which tricks the body into thinking there is no cancer in the body for the immune system to fight.

Results of a global medical trial, published in the prestigious New England Journal of Medicine, shows Pembrolizumab can also successfully treat lung cancer.

The trial involved 305 patients with stage four lung cancer from 16 countries, including Australia.

Approximately 70 per cent of the participants were still alive after 12 months of being treated with Pembrolizumab - some were in complete remission.

Co-author of the study and medical oncologist, Associate Professor Rina Hui from Sydney's Westmead Hospital says this drug has changed the way we treat the number one cancer killer in the world.

"The drug mobilises patients' immune systems to fight against cancer and performs much better than traditionial chemotherapy in some patients," Prof Hui said.

"I've seen widespread tumours shrink to nothing," she said on Monday.

Michael Gordon, a 65-year-old retiree from St Marys in western Sydney, was diagnosed with inoperable stage four lung cancer. He had a tumour the size of a golf ball in the middle of his chest.

Mr Gordon is now in remission after starting Prembrolizumab two-and-a-half years ago.

The father of two children, who continues to undergo treatment every three weeks via an IV drip as part of the trial, says the drug has saved his life.

"Without it I wouldn't have been here two years ago, I'm pretty sure I would have gone," he said.

Unfortunately the drug only works on those with high-levels of PD-L1, which equates to about one-third of all lung cancer patients, said Prof Hui.

While this drug offers some hope, Professor Sanchia Aranda, CEO of Cancer Council Australia says more follow-up on overall survival is needed to determine how effective this very expensive drug is at treating lung cancer.

"It's certainly not a miracle, it's another step in trying to advance our ability to treat people with metastatic lung cancer," she said.

Cancer of the lung is still the single most preventable cause of death from cancer and prevention should remain the focus of research efforts in Australia, said Prof Aranda.

"Of the 37,000 preventable cancers diagnosed every year in Australia, 15,500 of them are due to tobacco," she said.