As many as 40 percent of Māori and Pacific people with bowel cancer only discover they have the disease when they need emergency hospital care.
The figure is contained in new information about bowel cancer released by the Health Quality and Safety Commission today.
The data is provided by the commission in the form of an online Atlas of Healthcare Variation, for bowel cancer.
Key findings include that about a quarter of people with bowel cancer were diagnosed following a visit to a hospital emergency department, backing similar findings released last year in the Piper study.
However, 39 percent of Māori and 41 percent of Pacific people were diagnosed following presentation to an emergency department.
National Bowel Cancer Working Group chair Ian Bissett, an Auckland colorectal cancer researcher, said that was disappointing.
"It's disappointing to find this variation and to me what we need to be looking at is improving equity across service and care for patients right across the country. What we do see is variation between DHB [district health board] populations related to the demographics of their own DHB as well."
Bowel cancer is the most commonly reported cancer in New Zealand, with approximately 3000 cases and 1200 deaths a year.
Today's data showed that for a quarter of people the cancer was contained to the place where it had started, but for one in five it had spread to distant parts of their body by the the time of the diagnosis.
Two-thirds of people with bowel cancer had surgery in a public hospital and on average people stayed in hospital for 10 days after surgery.
On average, one in 20 people died within three months of surgery for bowel cancer. As well, more than two-thirds of people were alive two years after being diagnosed.
There was also an up to two-fold variation between DHBs for survival three months after surgery.
The commission advises caution in interpreting that data, as people are included in the DHB where they live but may have been treated elsewhere.
The Atlas data also reveals wide variations between DHBs over use of radiotherapy (long or short course before surgery) for those with rectal cancer, and up to a two-fold variation in surgery that usually results in a permanent stoma or bag for people with rectal cancer.
The commission said differences were a good starting point for asking questions about why people in different DHBs may get different treatment.
"When these questions are asked it can help DHBs improve their services."
Professor Bissett, a colorectal cancer researcher and surgeon, said the data contained in the Atlas was a major advance.
"I'm very excited that starting from national data sets we're able to produce quality measures of treatment across the country, indexed by DHB population, that tell us how we're doing at present."