Thousands of cancer patients could be denied access to life-extending drugs under new plans for approving medicines on the NHS, campaigners have said.
The National Institute for Health and Care Excellence (Nice), which decides which new medicines are cost-effective, is changing its criteria on how funding should be allocated.
The body's appraisal committees will now be asked to adopt a more "favourable approach" when considering treatments for people whose conditions represent a high burden of illness and where there is a wider impact on society.
The Department of Health asked Nice to look at the issue in order to ensure that the price the NHS pays for new medicines is more closely linked to their value to patients and the public as a whole.
In a consultation document published today, Nice has set out how it plans to achieve this aim, but campaigners said it amounts to a "stealth cut for cancer".
The Rarer Cancers Foundation said a move to abolish the criteria covering end-of-life drugs means there is no guarantee key treatments would be approved in the future.
It said the criteria is the reason why 12 specific life-extending cancer drugs have been approved by Nice.
Andrew Wilson, chief executive of the foundation, said the Department of Health's own figures show that up to 12,841 patients a year would have been denied the opportunity of treatment had the criteria not been in place.
He added: "The Government promised patients that they would be able to access the drugs their doctor recommended.
"Yet Nice's proposed reforms would be a backward step for cancer.
"Plans to abolish special rules for drugs used near the end of a patient's life have been slipped out in the small print of this consultation.
"They amount to a stealth cut for cancer and could have a devastating impact on access to life-extending drugs, with no guarantee that other changes to the rationing formula will compensate.
"Nice needs to come clean on the impact of these changes for cancer and reassure patients."
In the document, Nice said its plans for incorporating a new look at burden of illness "replaces the current approach in which our appraisal committees consider life extending treatments used at the end of life (the end of life treatments protocol)".
The new approach would see factors such as burden of illness, wider societal impact, non-health objectives of the NHS such as reducing the impact on carers and whether a new technology or drug is innovative, taken into account.
In the document, Nice said it intends to take the concept of burden of illness - the loss in quality and length of life - into account "more explicitly and systematically".
It will do this by measuring in quality adjusted life years (QALYs) the burden of a disease and comparing them with the QALYs that people would expect to have over the rest of their lives without the condition.
Nice also plans to assess societal impact by looking at the loss (or shortfall) in a person's capacity to engage with society as a result of living with a disease or condition, compared with if they did not have the disease.
It will focus specifically on the impact to society from the health lost by people as a result of their condition.
It said: "Since loss of good health affects a person's ability to engage in society, societal shortfall can be assessed by measuring the absolute QALY loss."
Chief executive of Nice, Andrew Dillon, said: " These proposed changes to the way we value new treatments will add further clarity to our recommendations and enable our independent advisory committees to explore more fully the potential these treatments have to improve outcomes for patients."
Paul Catchpole, director of value and access at the Association of the British Pharmaceutical Industry (ABPI), said: "The consultation recognises that the way Nice currently assesses medicines can be further enhanced to ensure better access to the most beneficial medicines for NHS patients.
"The current process is denying too many patients the medicines they should be entitled to and is now inappropriate for many of the new medicines pharmaceutical companies are currently developing for patients."
"We have a particular concern about the potential impact of incorporating Nice's existing 'end of life criteria' into the new system.
"We need to ensure that this does not lead to fewer medicines for patients at the end of their life being approved.
"There is currently an issue with Nice approving too few new cancer medicines which the new agreement must address."
A Department of Health spokesman said: "Better access to effective medicine is a priority for the Government, and it is absolutely not true to say that these proposals would reduce patients' access to life extending treatments.
"We appreciate that this is a complex proposal and raises some difficult issues - which is why we have asked Nice to find out what people think, but it is important to be clear that no decisions have yet been made."
Mark Flannagan, chief executive of Beating Bowel Cancer, said: "Any new approach that simply moves the goal posts will be met by dismay by cancer patients.
"Any system which doesn't lead to patients accessing latest cancer medicines is fundamentally flawed. It's accepted that access to new cancer medicines has changed the quality of life for thousands of cancer patients. Nice must listen to the views of patients and charities and create fair access which is right for a 21st century health system."