The Tánaiste Mary Coughlan has described as "shabbiness" the fact that almost 58,000 X-rays were never looked at by a radiologist in Tallaght hospital in Dublin for nearly five years.
One person's died and another's seriously ill undergoing treatment for cancer after their diagnoses were delayed as a result of the failures.
A helpline for patients has opened while an investigation into the issue is underway and the HSE is holding crisis talks at the hospital.
The Tánaiste admitted she wasn't fully informed, but that "there had been a failure of the system".
The Taoiseach Brian Cowen has denied that the Government or the HSE tried to cover-up the cancer scandal.
He made the remarks after Fine Gael leader Enda Kenny said it was the "best example of national failure on the part of the Government".
And Mr Kenny accused the Minister for Health Mary Harney of trying to suppress the scandal.