Smear test recalls after out-of-date vials error
The cervical cancer screening samples of 369 women in Wales were stored in out-of-date pots.
Cervical Screening Wales has written to the women telling them about the issue, and about half will need another smear test.
The programme, run by Public Health Wales, screens women for the HPV virus which can cause cancer to develop.
Less than 2% of women who received screening in Wales between July and October last year are affected.
Smear tests are carried out at GP practices, sexual health clinics and at hospitals. The sample is put into a vial containing preservative fluid, and returned to the Cervical Screening Wales laboratory.
It has been found that some vials used were past the manufacturer's expiry date.
Dr Sharon Hillier, director of screening for Public Health Wales, said: "We apologise sincerely to all women who will receive a letter from us related to this issue.
"I can reassure women that there is no evidence that any harm has been caused by this issue. We have looked carefully at all of the results issued already and where possible have rescreened samples.
"Anyone who has not received a letter from us has not been identified as affected by the issue, and does not need to be concerned or to contact us."
The incident took place at a time when Cervical Screening Wales was rolling out HPV screening - testing for the virus that causes nearly all cases of cervical cancer.
Women in Wales aged between 25 and 49 are invited for a smear test every three years; women aged 50 to 64 are requested to attend every five years.
Cervical Screening Wales invited 210,800 women for screening in 2017-18