Inspirational charity fund-raiser Stephen Sutton has said his cancer went undiagnosed for six months during its early stages.
The 19-year-old, who has raised more than £3 million during his three-year battle against multiple tumours, told the Daily Mail he still felt anger at his initial misdiagnosis.
Mr Sutton, from Burntwood, Staffordshire, told the newspaper: "On the whole, the NHS has been brilliant, but there will always be a kind of ... there always will be anger.
"If it had been caught earlier, it could have led to a better prognosis. It could have changed the situation. But even saying that, I'm not one to dwell on the past. It is what it is."
He was re-admitted to Birmingham's Queen Elizabeth Hospital at the weekend after telling his Facebook followers he had developed breathing difficulties.
The teenager, who has collected £3.22 million for the Teenage Cancer Trust, posted a picture of himself in hospital in April with a "goodbye" message.
But he made what he described as a miraculous recovery - coughing up a tumour and being discharged from hospital on May 2.
Commenting yesterday on his Facebook page - which has 750,000 likes - he wrote: "Unfortunately today I've ended up back in hospital. I had some breathing difficulties starting last night and after going to A&E have been admitted back to a ward for monitoring.
"I've still got the cough, then quite quickly developed a wheeze in my breathing and breathlessness upon any physical exertion.
"There's no immediate panic and I'm currently quite stable - I have been put on nebulisers and other meds which are currently helping my symptoms hugely."
The teenager was diagnosed with bowel cancer when he was 15. Despite treatment, his tumours spread and he was informed his condition was incurable in December 2012.
His fund-raising efforts have attracted support from celebrities including comedians Jason Manford, Russell Brand and Stephen Fry, as well as music mogul Simon Cowell.