This process will continue for the next few weeks, and 275 appointments are likely to be affected.
Cancer survivor Tracey Stevenson was due to see an oncologist on October 2, but her appointment at Christchurch Hospital has been cancelled.
She had a stage-3 tumour removed in June.
"I had a scan a few weeks ago and the radiologist told me there was a lymph node that was of concern to him, and that I'd need to be seen a little bit sooner.
"The cancer nurse tried to get me an earlier appointment, but that wasn't able to be done."
Stevenson was told to wait until October, but last week she got a call informing her of the cancellation.
"They couldn't give me any indication of when I'd get a new appointment."
The situation is particularly frightening for her, because if her cancer comes back it will most likely kill her.
"It's very scary knowing there's potentially some cancer growing in you that's not being dealt with.
"It may be nothing, but I don't know that. All I know is that they told me if my cancer returns it would be aggressive, and they wouldn't be able to cure me.
"They would just treat my symptoms for the rest of my life."
Stevenson slammed the cancellations as just not good enough.
"This is cancer, this is people's lives.
"It is life changing stuff - it's not an ingrown toenail."
For people as sick as she potentially could be, Stevenson said appointments need to be available and on time, or people could be missed.
"It's just horrendous, really."
Nightingale said the DHB was doing all it could to minimise the impact for patients and keep waiting time as low as possible.
"A waiting system for oncology appointments is being implemented to better maximise the department's current capacity.
"This will see patients waiting longer than usual for their appointments until the department is operating at full capacity again."
A range of urgent solutions are being explored beyond introducing clinical prioritisation, Nightingale said
These include up-skilling and redistributing trainees to cover increases in acute demand, urgent development of nurse specialist services to help manage patients in active care, exploring outsourcing options, and recruiting locums to assist.
But Nightingale is reluctant to lay blame for the delays on either the Covid-19 backlog, or ongoing Government pressure to cut costs at the DHB.
Canterbury has the highest deficit in the country at $170 million, and Crown monitor Lester Levy is working with the board to slash spending by $56.9 million this year.
The situation has seen also seen seven of the DHB's senior executive team members resign, and hundreds of hospital staff protest on the streets.
"It's important to note that this situation has come about due to unplanned staff leave and increasing demand, and is not in any way related to the DHB's savings plan."
Nightingale said it is also important to note during Covid-19 alert levels 3 and 4, the DHB's oncology service continued supporting all current patients - through a combination of telephone appointments, and minimal face-to-face appointments.
According to the Cancer Society, the cancellations at Christchurch Hospital are just a symptom of a nationwide problem.
Medical Director Dr Chris Jackson said cancer cases in New Zealand are growing exponentially.
"Over the course of the next 15 years, there will be a 50 per cent increase in the number of people needing cancer services.
"It's difficult for oncology departments to keep up with demand, everyone's been working at or near capacity for quite some time."
When services around the country are overrun with patients, reductions in staff - for whatever reason - puts extraordinary strain on the system, he said.
The solution lies in making sure services are well-funded - and increasing the focus on building the workforce in the years to come.
"Specialists don't just come from nowhere. They require a lot of training, and it takes a long time to get a specialist into a consultant post.
"You do need to have very long horizons, and unfortunately DHBs have been very focused on short-term needs rather than long-term planning."
But Jackson believes the newly-established Cancer Control Agency Te Aho o Te Kahu will help.
"I'm hopeful one of the things the agency will be doing is focusing on growing the oncology workforce - because that's clearly the priority."
