Jacinda Ardern believes it's unfair to compare New Zealand's cancer drug purchasing to that of Australia.
The Prime Minister was responding to backlash from cancer sufferers who feel let down by the Government's drug-buying agency Pharmac, which takes significantly longer to approve new drugs than Australia.
On Monday, host of The AM Show Duncan Garner, called on the Prime Minister to back an independent inquiry into Pharmac, initiated by cancer sufferer Wiki Mulholland.
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"In the time Australia has approved 24 new cancer drugs, we have approved, wait for this: none," Garner said.
Ms Ardern responded on Tuesday saying: "We spend almost a billion dollars making purchases on behalf of New Zealand. Some of the comparisons I've seen with Australia aren't necessarily fair."
Women stood on the steps of Parliament in October last year to present petitions to MPs calling for two important breast cancer medicines to be funded by the agency.
The women who protested in October, representing the group Metavivors, desperately needed funding and access for Ibrance and Kadcyla - life-extending drugs in the fight against advanced breast cancer.
Pharmac recommended funding for some of the drugs, but said they won't be available for everyone, with some advanced breast cancer sufferers not qualifying because they're already receiving other treatments.
The medicine costs only AU$40 a month across the Tasman, but more than $6000 in New Zealand.
Mother-of-three Ms Mulholland says Pharmac is too slow in its decision process of whether to fund new treatments, hence her call for an inquiry into how it operates.
Garner said the group Cango, which is made up of most non-profit cancer support groups, are demanding an inquiry into Pharamc and why New Zealanders don't get the best medicines to treat cancer.
Ms Ardern told The AM Show on Tuesday the Health Select Committee is currently responding to the petition that's been brought forward, which is "made up from politicians across Parliament".
She said New Zealand's drug buying agency has "been pointed to as being the envy of others" in that it "keeps it separate from politics, it bases decisions on evidence, and these are hard decisions".
"Politicians shouldn't do it," she said, noting that she personally knows someone suffering from cancer, implying her involvement could be a conflict of interest.
When confronted with the difference between Australia and New Zealand, Ms Ardern said Pharmac won't purchase the newest products on the market if they don't "add anything that a past product" already has.
"The important point to make is we can always make improvements to our health system. But I will always maintain the principle that I should not be the one making decisions about drug treatment in New Zealand.
"The select committee are free to do what they need to do."