The number of cancer patients turning to crowdfunding to pay for treatments not available on the NHS has soared, online donation platform JustGiving said.
Cancer patients and their loved ones launched 2,348 appeals on the website last year compared to 304 in 2015 - a seven-fold increase, the figures obtained by BBC Radio 5 live reveal.
The fundraisers generated £4,670,143 to help pay for private medical treatment at clinics in the UK and abroad, a significant rise from the £530,519 raised in 2015.
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Consultant oncologist Dr Clive Peedell described the number of patients bypassing the NHS as "very worrying" and said some may be trying to access treatments which are not beneficial.
"The NHS is clearly financially under pressure at present, but cancer therapy has received preferential funding compared to other diseases and conditions," he told BBC Radio 5 live Daily.
"The system for approving effective new cancer drugs is not perfect, but is much improved. The vast majority of proven effective treatments for cancer are funded by the NHS.
"This includes immunotherapy for a number of indications including lung cancer."
Dr Peedell added: "I worry that some patients may be trying to access treatment that may not be beneficial.
"Worse still, there may be significant extra costs involved, especially if patients pay privately or travel abroad."
Liz Sheppard, from Mansfield, Nottinghamshire, raised £135,000 online to help pay for private immunotherapy treatment after being diagnosed with small cell stomach cancer in November 2015.
The mother-of-three, who was given months to live after the rare cancer diagnosis, has already spent £60,000 of the money and is responding well to treatment.
She said: "If it wasn't for people's generosity and kindness, I wouldn't be where I am now.
"It's not something I could have self-funded. Without that money I wouldn't be here. It means everything."
NHS England said the immunotherapy treatment nivolumab was already available on the NHS for some cancers and is being considered by the National Institute for Health and Care Excellence (Nice) for others.
"Together with Nice we have also launched a new-look cancer drugs fund meaning patients will be able to access promising new and innovative treatments much quicker," it said.