Hospital errors which led to suspected cancer patients being discharged without being seen are "very worrying and clearly unacceptable", a health minister has said.
Dr Dan Poulter said patients deserve the best care after it was announced a £40,000 external review will examine what happened at West Hertfordshire Hospitals NHS Trust.
Two managers have been suspended after the trust admitted discharging hundreds of suspected cancer patients by mistake.
It said at least one person might have died as a result of the errors and 121 patients are yet to have their cases reviewed.
Dr Poulter said: " What has happened at West Hertfordshire Hospitals NHS Trust is very worrying and clearly unacceptable.
"Every patient in the NHS expects and deserves the very best care to give them the highest possible chance of surviving cancer. An independent review has been set up to investigate the issue urgently, and the Care Quality Commission will be monitoring the situation closely on the ground.
'The new and independent chief inspector of hospitals will be looking at the quality of care for patients - including cancer care - in his ongoing programme of inspections.
"This Government is also making the deliberate falsification of hospital records a criminal offence as part of our new emphasis on transparency and openness in the NHS."
West Hertfordshire Hospitals NHS Trust said that, in one case where a patient died, it was thought a delay in seeing them might have contributed to their death.
The trust is contacting the family of a second patient who has since died. That patient had advanced cancer at the stage the initial referral was made.
In another case, a patient had their diagnosis delayed due to errors but their cancer was found at the earliest stage.
Overall, 810 people have had their cases reviewed. Of these, 686 have been told there are no clinical concerns about the care they received.
The trust is made up of Hemel Hempstead Hospital, Watford General Hospital and St Albans City Hospital. Errors are believed to have happened at all three sites.
The mistakes came to light when new managers found flaws in the process for patients being seen after referral by their GP or dentist.
Patients who missed their first appointment and were recorded as not showing up were discharged by the hospital. NHS rules say patients should always be offered a second appointment.
The patients had been referred for urgent appointments by doctors between January 2010 and November 2013.
The trust announced today that a £40,000 external review is being carried out by four authorities, including NHS England and the Trust Development Authority.
It said it had offered patients "our apologies for any anxiety and distress" caused by the events and had implemented a new IT system to track each patient's appointment, missed appointments and cancellations.
Trust chief executive Samantha Jones said: "It is absolutely clear that the trust was not always following the correct administrative processes for these patients and we let them down.
"These concerns date back a number of years and were identified as part of the new management team's commitment to improve the way we administer and manage patient care.
"I would like to apologise to each and every patient who has been affected and particularly to the relatives of those who have since died.
"We have of course made significant changes to help prevent this ever happening again and will share the outcome of our investigations with those affected and with the wider public."
Geoff Brown, chief executive of Hertfordshire Healthwatch, said: "We were of course very concerned to hear about this incident and it will undoubtedly cause upset and distress for many patients and their families.
"The trust's management team has kept us informed during the review and we are pleased to have helped them in shaping the communications they have sent to patients and their families.
"We are confident they are working hard to support people who are concerned or worried and hope to see a speedy conclusion for the 121 patients whose cases are still being reviewed."
Hemel Hempstead Conservative MP Mike Penning said: "I am shocked to learn that Hemel Hempstead cancer patients have been allowed to slip through the net due to the incorrect use of procedures. They have been badly let down and it is very upsetting.
"A national review is needed to make sure that the problem is not being repeated elsewhere and that no more patients are let down in this way.
"I commend current chief executive Samantha Jones and her team for discovering the problem and facing it head on to ensure that no more patients suffer the same breakdown in their care."
The trust said it is "confident" it has contacted everyone affected by the errors but anyone concerned should contact their GP or call the trust's information line on 01923 217100.