1,200 medical cases from Noble's Hospital have had to be reviewed after 'a matter of serious concern' in the radiology department.
The Department of Health and Social Care has confirmed patients who attended assessments in the breast clinic between 2015 and 2017 may not have had necessary investigations.
As a result of this an external review was commissioned to check all the cases seen by the one radiologist concerned.
The radiologist is no longer employed at Noble's Hospital.
The department has apologised to all women concerned and their families.
Minister David Ashford says: "The external review has been rigorous and complex.
"In total, more than 1,200 cases have been reviewed by radiologists at centres in the UK, with expert opinions sought in each and every case.
"This process has unfortunately taken longer than wished or expected, largely due to the complexities involved in commissioning this volume of work.
"It was however, vital to gain a comprehensive understanding of the issues we face, in order to respond appropriately to our patients."
Letters have been sent to all of the women involved – 26 women will be recalled for additional assessment.
A special helpline has been set up on 01624 642400.