John Key is not ruling out overriding Pharmac to fund cancer drug Keytruda, but says choosing which drugs to fund is a "balancing act".
The Prime Minister, appearing on the Paul Henry Show this morning, said the debate around the funding of Keytruda, or Pembrolizumab, was "very emotional".
The drug is used to treat melanoma and is considered by some cancer specialists to be the greatest advance since chemotherapy. It is state funded in both Australia and Britain.
Mr Key told Paul Henry the drug could "potentially" be funded, but said he preferred not to override Pharmac.
"I can't say we'll override the ruling from Pharmac - our preferred option is always for Pharmac to make the right decision and get there.
"It's very difficult... it clearly works for some people and for others it doesn't.
"What they are saying is, on the budget they have at the moment in theory there are some other drugs that are better."
The drug could be funded if health was allocated more money, he said.
"We can't override Pharmac easily, but if we give them more money they might."
When questioned by Henry about the potential of patients dying while waiting for Keytruda to be funded, Mr Key responded: "Trust me when I tell you we want to help these people.
"We desperately want to save them. There are lots of drugs and lots of them are expensive."
He said scientific advances meant new drugs were being released rapidly, which meant Pharmac had to make difficult decisions about what to fund.
"I know people will say we did that for Herceptin and we did, we campaigned on it and we did it.
"If that's the way we make the decision, then by next year, because of the wonders of modern science, there will be another drug that will come along. Not necessarily in melanoma, but in something else. That's the balancing act here."
Pharmac's experts committee last week granted it a low-priority status because of uncertainty about its benefits and its high cost - about $300,000 a patient for two years' treatment.
Former US president Jimmy Carter this morning announced he was cancer-free, following treatment with Keytruda.
Labour leader Andrew Little and health spokeswoman Annette King have pledged to fund Keytruda if Labour is elected in 2017.
