The health watchdog is to carry out an "urgent" inspection into the treatment of breast cancer patients at a debt-ridden NHS trust.
Regulator Monitor said concerns had been raised about faulty tests conducted on patients at Sherwood Forest Hospitals NHS Foundation Trust.
The Trust is to recall 79 women with regard to the results of breast tissue biopsies.
A Monitor spokeswoman said the Care Quality Commission (CQC) will begin the inspection immediately.
The team will look at breast cancer screening, pathology and clinical governance at the Trust.
The CQC will also conduct a "deep dive review" to ensure there are no concerns about standards of patient care in any other department at the Trust.
CQC chief executive David Behan said: "This urgent inspection will allow us to take an in-depth look at the quality and safety of the Trust's services that relate to breast cancer screening.
"The action we are taking, alongside Monitor's intervention, will ensure that both regulators have a good picture of the quality and safety of the Trust's services and the robustness of its governance."
In September, Monitor announced that it was taking regulatory action against the Trust because it lost £6 million in the first three months of the financial year. The Trust, which is grappling with private finance initiative (PFI) repayments, was found to be in "significant breach of two terms of its authorisation", Monitor said.
Sherwood Forest, which was awarded Foundation Trust status in 2007, serves a population of 418,000 people across Nottinghamshire as well as parts of Derbyshire and Lincolnshire.