An investigation has found no overall failure by the Otago-Southland breast-screening service in regard to the delayed detection of cancer in 28 women.
The Health Ministry report, released on Wednesday night, says women can continue to have confidence in the service.
The ministry launched the investigation after a radiologist suggested a cancer diagnosis for the women might have been delayed between 2007 and 2010.
The report says the 28 women did receive a false clearance - known as a false negative - after their routine mammogram and were not recalled for a check at that point, so their cancer was not discovered until the next mammogram two years later.
The report says screening doesn't diagnose cancer but provides a statement of probability, and there are always false negatives.
It says 28 such cases during a period when 32,000 women were screened is internationally acceptable.
The report was reviewed for the ministry by the chair of BreastScreen Aotearoa's independent monitoring group.