A women's health group says it is pleased an urgent investigation has begun into a possible delay in diagnosing breast cancer in Otago and Southland.
The Health Ministry says 28 women in Otago and Southland may have had their breast cancer diagnosis delayed.
The ministry says it appears to have occurred over a three-year period until 2010, and it has launched an investigation.
It says extra checks have been implemented in the screening process.
The Federation of Women's Health Councils says some cancers will always go undetected in any screening programme no matter how good it is.
But it says the investigation must be thorough with its findings made public and any problems acted on immediately.
The DHB has not commented but has set up a hotline - 0800 214 579 - for any one concerned.
The chief medical officer at the ministry, Don Mackie, says it appears initial mammograms the women had under the nationwide free breast screening service failed to flag the existence of a possible malignancy.
"These are women who have been diagnosed with cancer, and on retrospective review of their films the question is whether or not the cancer was diagnosed promptly at the early opportunity of screening."
Dr Mackie says subtle signs of cancer may have been missed, and the ministry has launched a system-wide investigation Thursday into BreastScreen Healthcare, the breast screening service provided to the Southern District Health Board.
The investigation was sparked by a staff member's concerns.
Breast Cancer Aotearoa Coalition chair Libby Burgess says it is worrying that cancer might have been detected earlier in such a large number of women in one region.
The Breast Cancer Foundation says the needs of the women affected must take priority.