A Westcountry hospital could face a formal investigation after cancer patients urgently referred by their GP waited too long for treatment.
The Royal Devon and Exeter Hospital (RDE) has missed a key 62-day maximum wait for nine months and is at risk of breaching its licence.
Monitor, the health service watchdog, said it was gathering evidence and was considering launching an inquiry into the trust's performance.
A spokesman for RDE said they were working hard to make sure targets were hit.
"Extensive action has been taken across the trust and within each cancer speciality over the last nine months," he said.
"This includes creating some additional outpatient and surgical capacity and, importantly, changing the way we work to streamlining the management of patients throughout their cancer treatment pathway."
He added that the signs were that the action plan had been a success.
"The improvement work is now starting to take effect such that the 62-day target was achieved in June (20)13 and is well on course to be achieved in July (20)13."
All NHS trusts are subject to strict Department of Health issued guidelines for the maximum amount of time patients should wait for treatment.
In January it was reported to the RDE board that four cancer targets had not been met in the previous three months.
One target – that patients should receive subsequent treatment within 31 days – was breached because of an administrative error in the plastic surgery department.
The RDE spokesman said this had been resolved and no patients came to harm as a consequence of the delay.
Papers presented to the board said the "single biggest impact" on the missed 62-day referral to treatment target was the purchase last year of a £2.5million DaVinci robot used to treat prostate cancer.
It said that more local patients had been expected to be treated at RDE, but the influx of patients from North Devon and Torbay was "not fully anticipated."
Many of these referred patients were "a point where they are very close to, or beyond their 62-day breach date," the papers added.
The DoH target states that 85% of patients should be treated within 62 days of an urgent referral.
But according to board papers, at its lowest point just 79.6% of patients were treated within that time limit.
The spokesman said the number of patients affected was "relatively small", around six patients a month, a number of whom had missed the target by less than a week.
A spokesman for Monitor, which regulates Foundation Trust hospitals, confirmed it was examining issues surrounding missed cancer targets at RDE.
A spokesman said: "We would like the trust to improve their performance, but in terms of opening an investigation, we are still gathering information in order to make a judgement."