The Minister for Health, Mary Harney, has ordered a full report into the treatment of a cancer patient who was diagnosed with breast cancer 14 months after she had been given the all-clear.
Cork University Hospital has apologised to 41-year-old Rebecca O'Malley who lives in the Lough Derg area.
The Health Service Executive said it is reviewing a further 300 cases.
Ms O'Malley had a breast removed last summer, 14 months after she was given the all-clear. The hospital says a full review is under way. Ms Harney said the review needs to be completed as soon as possible.
All the cases being reviewed relate to breast cancer tests sent from the Mid-Western Regional Hospital in Limerick to be tested at Cork University Hospital.
She said she will then determine if there is a need for an external evaluation of what happened at CUH.
Speaking on RTÉ Radio's Morning Ireland, Mrs O'Malley said she was initially encouraged not to go public about the mistake.
A HSE spokeswoman said if any woman has concerns she should contact the breast cancer clinic at the Mid-Western Regional Hospital in Limerick on 061-482796.
They can also contact Cork University Hospital on lo-call 1800-742800.