Some New Zealanders are probably walking around with undiagnosed cancer after they were withdrawn from a screening programme.
Bowel Cancer New Zealand spokeswoman Sarah Derrett said it was unacceptable that warnings were ignored about the system not working, and asked what was being done to track 10,349 people who were "uncontactable".
More than 12,000 people were inappropriately withdrawn from the Waitemata bowel screening pilot programme because their addresses on the National Health Index were not current.
Since then, 2441 people have been tracked down and eight cases of bowel cancer diagnosed.
Waitemata District Health Board raised concerns with the Ministry of Health about the register over several years.
"It seems the plan is simply to re-invite these people when, and if, their address is updated," Derrett said.
"There needs to be action taken now to trace this large missing group – among which there are likely to be people with undiagnosed bowel cancer.
"It is imperative this is addressed without delay."
Eight people who had updated addresses but not been invited to participate were later found to have cancer.
A clinical review of the cases found that for five of the eight (two of whom had died) screening would not have altered their clinical outcomes.
For the other three, including one who had died, earlier diagnosis was in their best interests, but it was not possible to determine if screening would have improved their prognoses.
The full national bowel screening programme is being introduced across the country over the next few years.
Derrett encouraged open discussion about bowel cancer with medical professionals and avoiding "sitting on your symptoms".
Those who don't live in DHB screening areas or have symptoms or a family history of bowel cancer and want regular checks can talk to their GP or buy a commercially available bowel screening kit, which involves the family doctor, at Life or Unichem pharmacies.
When announcing a review of the national bowel screening programme in February, Health Minister David Clark apologised for the invitation botch-up, and outlined the efforts to contact and re-invite about 2500 people who had been withdrawn but had since had their addresses updated in the NHI.
The independent review of the programme, ordered by Clark and led by Professor Gregor Coster is to report back in June.
It will explore the pilot invitation issue, whether the programme is likely to be successful, and what changes might be required.
• Bleeding from the bottom or seeing blood in the toilet after a bowel motion
• Change of bowel motions over several weeks without returning to normal
• Persistent or periodic severe pain the abdomen
• A lump or mass in the abdomen
• Tiredness and loss of weight for no particular reason