Two drug companies have attacked a decision to remove their treatments from a fund designed to give access to expensive therapies in England.
The Cancer Drugs Fund is overspent and 42 drugs are being reassessed as price caps are brought in for the first time.
Pharmaceutical companies say they are "outraged" at a "fundamentally flawed" decision that will damage patient care.
NHS England said the current system was unsustainable and that there were new drugs "that will do more for patients".
Drugs have to be cost-effective for the NHS to make them routinely available.
Prime Minister David Cameron set up a separate pot of money in 2010 to give patients access to expensive drugs, irrespective of cost.
The £280m-a-year Cancer Drugs Fund is hugely popular and has been used by about 55,000 people.
But as things stand it expects to be £100m over budget by the end of the financial year.
A full NHS England announcement on which drugs are being struck off the approved list is expected on Monday, but rejected drugs companies have started to break ranks.
Sanofi says a prostate cancer drug, Jevtana, is being pulled.
Zaltrap, a bowel cancer drug that can extend life after a tumour has spread, has also been removed.
Tarja Stenvall, the company's general manager, said: "We are hugely shocked and disappointed at this decision against Jevtana.
"We believe NHS England's process for reviewing drugs currently listed on the Cancer Drugs Fund has been fundamentally flawed.
"It was arbitrary, inflexible and relied on very questionable evaluation criteria that were not independently verified or endorsed."
Meanwhile, Eisai has been informed that its breast cancer therapy Halaven will no longer be paid for by the fund.
Company president Gary Hendler said: "To say that we are disappointed by this decision would be a gross understatement, we are outraged.
"We now call on the government to stop this arbitrary removal of drugs."
Any patient currently having a drug paid for by the fund will not be affected by any changes which come into effect in March 2015.
Professor Peter Clark, an oncologist and chairman of the Cancer Drugs Fund, said: "We need to get maximum value for every pound we spend".
"We can no longer sustain a position where we are funding drugs that don't offer sufficient clinical benefit when drugs that will do more for patients are coming on stream."
At the same time as reassessing 42 current drugs, the NHS is also evaluating 12 new therapies.
The decision to introduce price restrictions has provoked a mixed reaction from cancer charities.
Some say it is "deeply concerning" and will damage patient care while others say the fund has created "perverse incentives" that meant drug companies did not need to make their medicines affordable and that a long-term replacement for the fund was the real issue.
Eric Lowe, chief executive of Myeloma UK, told the BBC: "Our feeling is the Cancer Drugs Fund is not sustainable, it's a policy anomaly and we don't understand why the Conservatives and Labour are intent on continuing with it in some form.
"The drug companies have behaved badly with their pricing and we support the Fund going back to try to reduce costs."
Dr Mangesh Thorat, from the centre for cancer prevention at Queen Mary University of London, said: "This issue presents me with a dilemma.
"As a cancer clinician, I am happy that this Cancer Drugs Fund prevents my patients from being denied treatments towards end of their life, however, on the other hand I think this fund not only undermines NICE, but also discriminates against patients in similar situations who have diseases other than cancer."