Cancer patients who should have bone marrow transplants within four weeks are waiting for four months - or longer - because services are overloaded.

Doctors and advocacy groups warn those delays could be deadly and they are disappointed at the lack of action from the Cancer Control Agency.

NZ man Mark was diagnosed with multiple myeloma - a cancer of the white blood cells - in March 2017.

He had his first bone marrow transplant right on schedule in September that year, but relapsed at the end of 2020.

Doctors said he would need another transplant by July 2021.

"We'd been given a couple of two week warnings, they get you in a couple of weeks early and do a bunch of tests on you. But then we were pushed back and heard nothing."

At one stage he was about to have his transplant when he caught Covid and got bumped off the list again.

"And then that stretched out and I didn't get my transplant until 2022, September 2022."

Multiple myeloma - which dissolves the bones - usually affects people in their 70s, but Mark was just 51 when he was diagnosed.

He is keeping as fit as he can in the hope he will not need another transplant for a couple of years, especially as the wait times have got worse.

But he worries that the wait for the last one has already hastened the disease's progress.

"Since then I've had another scan and they've found a lesion on my hip which is a new one. So possibly that delay has thinned my bones even more.

"I can't fault the staff, the nurses and doctors and everyone are so committed. But you know they're frustrated too."

Consultant haematologist Professor Peter Browett says waiting times for transplants have become acute in the past two and a half years.

That's partly due to increased demand from an ageing population.

Six years ago, the team in Auckland was doing 50 to 60 transplants a year.

"Now [they're] transplanting in the adult setting around 120 patients per year but there hasn't been an equivalent increase in the resourcing, the staff and facilities to look after those increased numbers of transplant patients."

Professor Browett, who is also medical director of Leukaemia and Blood Cancer New Zealand, says some patients can afford to wait longer than others, depending on the type of cancer they have.

Those with acute leukaemia need transplants within four to six weeks of chemotherapy, but they are often waiting three or four months before there is "an available slot".

"And so that's the group of patients who are disadvantaged, who are needing further treatment and are at risk of their disease recurring before we can take them through to transplant."

Professor Browett says clinicians have been involved in lots of discussions in the last couple of years at local and national level over the need for more staff and patient beds - and on concrete plans to make this happen.

"But as yet we haven't seen actions from that plan that's been developed by Te Aho the Cancer Agency."

Te Aho o Te Kahu, the Cancer Control Agency, says officials have been working closely with the sector since becoming aware of delays for stem cell transplants in 2021.

In a written statement, chief executive Rami Rahal says the agency is monitoring wait lists, developing business cases for future investment in staffing and facilities, and working on national care standards.

"It is concerning there remains delays for people accessing stem cell transplants.

"Timely access to high quality stem cell transplant is an important treatment option for people with blood cancer, and we remain focused on supporting Te Whatu Ora and the wider health system to ensure wait times are addressed and people receive care more quickly."

Professor Browett says this response is "very disappointing", considering there have been more than two years of meetings and discussions.

-Ruth Hill/RNZ.