More than 1,700 patients at risk over NHS mail blunderpublished at 08:34 British Summer Time 27 June 2017
Officials said the number was likely to rise, as a third of the 700,000 cases identified had yet to be reviewed.
Cancer test results, child protection notes and medication advice were among the notes that went missing.
The National Audit Office also said there were serious questions to answer, external about the handling of the incident.
The company, NHS Shared Business Services (SBS), was employed in the East Midlands, South West and north-west London to redirect mail for the health service.