A health trust boss apologised today after it was disclosed eight women were being treated for breast cancer after they were previously given the all-clear.
North Cumbria University Hospitals NHS Trust temporarily suspended its breast screening service last month while a major review was conducted into tests involving about 1,600 patients.
Concerns were raised over cases from April 2007 where women were called for a second screening following routine mammograms.
A total of 1,477 of the tests have so far been reviewed, with 1,302 not needing any further assessment, the trust said.
Some 130 patients were told they would benefit from more checks and of these 49 have been consulted to date.
A trust spokeswoman said: "Of the 49 women so far recalled who would benefit from a further assessment, 40 require no further treatment.
"Eight patients require treatment for breast cancer and one patient has DCIS (non-invasive pre-cancer). Of the eight patients requiring treatment, three have already started treatment; three have planned treatment and two are having a treatment plan and options developed."
She added the trust was working closely with NHS Cumbria to quickly restore the screening programme which calls women aged between 50 and 70 for routine three-yearly mammograms.
Carole Heatly, chief executive of North Cumbria University Hospitals NHS Trust, said: "Our trust fully understands and appreciates the distress and anxiety this issue will have caused and apologises to all concerned. We are undertaking every measure possible to ensure that we provide the best high-quality service."
Meg McArthur, senior policy officer at Breakthrough Breast Cancer, said: "Any type of misdiagnosis is extremely worrying and we hope that appropriate measures are put in place as soon as possible to reassure women and to ensure that this does not happen again.
"We hope that it doesn't put women off attending their screening appointment, as early detection offers the best chance of a successful outcome.
"The NHS Breast Screening Programme is an important service that is estimated to save 1,400 lives annually in England alone."
A helpline has been opened since the review which is available from Monday to Friday 9am to 5pm on 01228 608289.