At least 18 serious cases are being investigated by NHS bosses after GP and dermatology services were stripped from private medical company.
The Kent and Medway Clinical Commissioning Group (CCG) confirmed on Monday an independent review was taking place.
It will see if delays to treatment for thousands of patients using DMC Healthcare services "caused harm".
DMC was responsible for nearly 60,000 patients at nine surgeries in Medway, and skin condition services in other parts of Kent, the Local Democracy Reporting Service said.
In north Kent, there were 1,855 patients needing urgent treatment and a further 7,500 on the dermatology service waiting list.
Of those, 700 had been waiting more than a year.
Medway Council's health scrutiny committee chairman David Wildey said the decision to allow DMC to take control of key health services was a "total failure".
Nikki Teesdale, from Kent and Medway's CCG, said it was "too early" to reach definitive conclusions around the 18 serious cases.
Speaking to Kent and Medway's joint health scrutiny committee on Monday she said of the 18, five had been waiting "significant periods of time" for cancer services.
"Until we have got those patients through those treatment programmes, we are not able to determine what the level of harm has been," she added.
When DMC's contract was suspended Sussex Community Dermatology Service (SCDS) took over responsibility for its patients.
Since then waiting list has reduced from 7,500 to 800, thanks to more consultants being brought in and extended services at other clinics around the county.
Ms Teesdale admitted the DMC service had gone "significantly wrong" but assured the committee CCG bosses were satisfied with the emergency contractor.
At the time, DMC Healthcare said taking over the services had been too "too much".
A final decision over the long-term contractor has yet to be made.