The Breast Cancer Foundation is demanding approval granted for a new drug be extended to those already receiving treatment.
Funding for the drug, known as Perjeta, was part of a deal "worth tens of millions of dollars" announced today by drug-buyer Pharmac.
Pharmac said the deal included nine medicines, covering 10 different conditions, and funding of three new treatments.
The deal would give 2000 people access to medicines for a range of conditions over five years, Pharmac said.
It includes funding for three new medicines to be available from January, including Herceptin, chemotherapy for those newly diagnosed with aggressive breast cancer, and Perjeta which battles breast cancer which has spread.
Current Medsafe registration, however, meant the drug - also known as pertuzumab - could only be given to those who had received no other treatment.
Breast Cancer Foundation chief executive Evangelia Henderson said that meant 160 women already on Herceptin would be excluded.
She said that was heartless.
"Yes, there's debate about the statistical evidence for this group, but it's an argument that will never be resolved, as the original trial didn't set out to measure the effectiveness of Perjeta for people already on Herceptin."
Pharmac acting chief executive Sarah Fitt said Pharmac was "still working though" the issues raised by the foundation and others regarding access.
"So at the moment it's mainly used in combination with other medications - Herceptin and Docetaxel. There are some groups of patients who are not eligible for treatment at the moment but we are having further discussions with our cancer specialists early in the new year to look at those other groups of patients."
She said breast cancer was the most common cancer affecting women in New Zealand, and funding of Perjeta, in combiation with Herceptin, would go a long way towards improving patient outcomes.
Breast Cancer Aotearoa Coalition spokesperson Libby Burgess said Perjeta was an effective drug that offered an average 16 months' extra life for those with the advanced, HER-2 positive breast cancer.
"They're going to be spending an extra 16 months with their families," she said.
"And that makes a real difference if you have young children at home. It makes a difference for anybody. I mean, this is a totally breakthrough cancer medicine."
Dr Burgess also hoped the criteria barring wider access would be changed early next year.
She said that when Australia funded the drug from 1 July last year it had "reached back" for a year and funded it for women who had been diagnosed up to a year prior.
Pharmac had already received a lot of feedback saying the drug should be more widely available here as well, she said.
"Pharmac is going to go back to its advisory committee PTAC to discuss this to get more information and evidence around that. So it's not off the table yet."
Roche New Zealand general manager Daniel Thurley said it was a big day for everyone.
"What we really ought to be celebrating today is the thousands of patients who, from this deal, are going to get access to medicines which for many of them will mean that this is the difference between seeing next Christmas and not."
The other new medicines funded under the deal are obinutuzumab, or Gazyva, for chronic lymphocytic leukaemia, and pirfenidone, or Esbriet, for idiopathic pulmonary fibriosis.
Access has also been widened to Pulmozyme for children under five with cystic fibrosis, and to rituximab (Mabthera) and tocilizumab (Actemra).