The Welsh Government does not believe a breast cancer screening error has affected them even though they used the same IT system as England, according to Jeremy Hunt.
While it's well-known that a lump in the breast could be a sign of the disease, there are many lesser-known symptoms that women (and indeed, men) should be aware of, as treatment is more successful if it's detected early.
Hunt said: "The existence of a potential issue was brought to the attention of the Department of Health and Social Care by Public Health England in January, although at that stage their advice was that the risk to patients was limited".
He said: "This awful blunder may have resulted in tragic consequences for so many families and I have contacted the Morecambe Bay trust to find out whether any local women have been affected".
Women who are concerned about whether they had missed a screening can call 0800 169 2692.
Ms Thomas said: 'It's absolutely critical we understand what happened and make sure this situation never happens to another person again.
Up to 270 women may have had their lives cut short after the NHS failed to invite them to breast screenings, the Health Secretary has said.
AgeX was created to examine whether screening should be extended from the current age range of 50-70 to include those aged between 47 and 49, and between 71-73.
Patricia Minchin, 75, said she was not offered a screening in 2013 when she turned 70, and is battling breast cancer.
The error remained undetected for eight years until Public Health England - which oversaw the program - discovered the problem after it began analysing data from the screenings. "We anticipate that all re-screens will be completed by the end of October 2018 and extra capacity is being identified so that routine screening will not be affected".
An independent review is expected to be launched into the error, which dates back to 2009.
There are unlikely to be more fatalities than that - but the Health Secretary said the true number could be less.
The most recent figures show there were 2,786 breast cancer cases in 2015 in Wales.
She said: "Anything that is going to cause more distress and worry and potentially cause women long term problems is really not a good thing".
Letters will also go to next-of-kin of patients who did not get their invitation and have died. We must also recognise there may be some who receive a letter having had a terminal diagnosis.
On Wednesday Mr Hunt said "administrative incompetence" meant some families may have lost, or may be about to lose, a loved one to cancer.
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