Thousands of cancer screening test samples are being reviewed after an issue was discovered in a laboratory.
Basildon and Thurrock NHS Foundation Trust said 2,500 samples from cervical cancer tests were being re-screened after an issue was identified in the lab run by Pathology First.
An investigation was launched following a routine visit from Public Health England in June last year.
The lab has arranged for the samples, which were reported as negative, to be re-screened independently.
Since then, 900 samples have been reviewed, and 17 women have been invited for further assessment.
Of these, nine women need to be re-screened while eight have been referred for further investigation.
The trust said: "We understand that this is a potentially worrying time for the women involved and would like to reassure all women covered by the locally provided cervical screening programme that this was an isolated incident."
Pathology First delivers laboratory services to around 750,000 patients and more than 100 GP practices in the South East.
The lab in Basildon, Essex, carries out more than 900 different types of test.
The affected samples were taken between April 2016 and September 2017 from women between 24 and 29 who were undergoing their first smear test, and a number of women in their 60s.
NHS England said there have been changes to local processes and updated staff training to ensure women receive safe, high-quality screening.