The Health Service Executive has said that reviews of cancers were conducted in the BreastCheck programme that were not part of a standardised audit process.
An expert group is examining issues related to the matter and an interim report is expected soon.
Reviews of what are known as "interval cancers" were conducted in different locations, as part of education and accreditation for clinical staff.
Interval cancers are cancers diagnosed in between routine screening episodes.
The HSE said that if a review was requested by a woman, then it was part of a structured approach and the woman and clinician would have been informed of the results.
In his September 2018 report, Dr Gabriel Scally noted that the BreastCheck charter did not make any reference to open disclosure.
The unstructured reviews of mammograms, which are part of the accreditation processes, are what the expert group is examining.
In a statement, the HSE said that an expert group in BreastCheck "is considering historical processes".
The review began in December 2018 and an interim report is expected by autumn.
The expert group is examining the basis on which the information for reviews of interval cancers was gathered, if it should be disclosed to patients and how that would happen.
The HSE said that until such time as the expert review is complete, it was not prudent to speculate on or predetermine any findings or recommendations from the work of the group.
Interval cancer training and education was a mandatory requirement to obtain the accreditation process, the HSE said.
The HSE said that interval cancer rates are a very important measure of all breast screening programmes and that the Irish programme interval rates were comparable to, or better than, other published programmes.
There are three types of interval cancers;
- Newly detectable cancers that have developed since the last screening appointment. These are common.
- Cancers that were visible at the last screen, but not recalled for further tests because the signs of cancer were very subtle and thought to be normal. These are less common.
- Cancers that were visible at the last screen, but not recalled for further tests because the signs were missed. These are reportedly rare.
The medical literature says that interval cancers occur in around three in every 1,000 women screened and that the majority of these cancers were not seen at the previous screen.
The BreastCheck Screening Programme was established in 2000 and all women between the ages of 50 and 67 are invited to take a mammogram every two years.
From 2000 to February 2019, BreastCheck has provided more than 1.9 million mammograms to more than 570,000 women and detected more than 12,000 cancers.