Immunotherapy drugs like Keytruda could well be the future of cancer treatment, experts say.

Keytruda, and counterparts like Opdivo, have been described by many as "miracle drugs" for their ability to cure people of what would previously have been considered terminal cancers.

Earlier this week the Herald spoke to two lung cancer patients who had both been given months to live but were now looking to the future, thanks to their tumours shrinking just weeks after starting treatment with Keytruda.

Since then other cancer patients have come forward to share the remarkable results they had seen after using the drug to treat terminal bowel and liver cancers.

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Father-of-four Jack Davis is one of them. He had beaten cancer twice before but this time it wasn't looking good.

Doctors told the 49-year-old Christchurch man he had terminal bowel cancer and had two to six months to live - that was in May.

Just over six months later, the tumours in his small intestine neck, stomach wall, lymph nodes of the neck and stomach nodes have all halved in size thanks to Keytruda.

Instead of the palliative chemotherapy he was offered in the public system, he opted to pay for Keytruda and received his first treatment almost 12 weeks ago.

"It's remarkable. It's a miracle drug," wife Sally-Anne said. "We're on top of the world...He should have been dead by now."

Jack Davis, back right, has seen his bowel cancer halve in size thanks to Keytruda. Pictured here with wife Sally-Anne and their four children. Photo/Supplied
Jack Davis, back right, has seen his bowel cancer halve in size thanks to Keytruda. Pictured here with wife Sally-Anne and their four children. Photo/Supplied

Otago University cancer genetics laboratory director Professor Parry Guilford said there was nothing showing as much promise in the treatment of cancer as immunotherapy drugs like Keytruda.

"We are seeing genuine cures of people with advanced diseases," he said.

He said targeted treatments being developed had seen remissions but no cures.

He said researchers were now considering and testing how other treatments could be used in conjunction with immunotherapy drugs to create even better results.

"It's changing our thinking...Keytruda has certainly changed the game."

New Zealand Cancer Society medical director Chris Jackson agreed it was an exciting area of emerging research.

"There's more hope for people diagnosed with cancer than ever before."

Keytruda was being used to treat melanoma, lung, bladder, kidney and colorectal cancer with incredible success as well as being used with more modest success for other cancers including liver, head and neck and other types of skin cancer.

But for every day Kiwis faced with a terminal cancer diagnosis, the drugs often remain out of reach.

For Jack Davis, it came at a cost - $9800 for the drug every three weeks.

They have raised the money through family and friends on Givealittle, sold things they don't need and are considering re-mortgaging their house to cover the cost of the treatment.

But Sally-Anne said they were the lucky ones who had been able to scrape the money together.

"It should be Government funded. They need to step up. There's other people out there that don't know how to obtain the drug or how to fundraise for it. How many people have to die?," she said.

The treatments cost tens of thousands of dollars and are only publically funded for people with melanoma.

Guilford said he did not expect that to remain the case for long because every drug company would be looking to get involved in immunotherapy treatments, which would inevitably lead to more competitive pricing.

There were more than 100 clinical trials using immunology drugs going on around the world at the moment he said.

Jackson said a review of Pharmac's processes were needed to allow sick people access to promising new drugs in a timely manner.

The process needed to have some time frame on it, be more transparent and allow more engagement from the medical community.

An early access scheme should also be considered to allow sick people to gain temporary access to drugs, which could save their lives while Pharmac negotiated with the manufacturer to get the best price.

New Zealand's drug funding agency, Pharmac, was in the process of reviewing an application for funding Keytruda for lung cancer and for funding Opdivo for the treatment of a kidney cancer.