Bone marrow cancer patients in England and Wales have been denied a life prolonging drug, available in Scotland.
Treatment costs about £18,000 per patient
The NHS's drugs watchdog has released guidance which says Velcade's cost-effectiveness has not been proven and more research is needed.
Patients and health charities have condemned the ruling by the National Institute for Health and Clinical Excellence.
Velcade slows the advance of myeloma - cancer of bone marrow plasma cells.
An announcement from NICE had not been expected until Tuesday, but it was brought forward after the ruling was apparently leaked to the press.
Last resort drug
Andrea Sutcliffe, who led the drug appraisal, said she was concerned at "misleading coverage" in some national newspapers.
"It is one thing to criticise our decision not to recommend the use of this drug, but quite another to unfairly raise patient expectations about the effect of this drug and its availability in other parts of the UK," she added.
Around 4,000 people are diagnosed with myeloma in the UK each year.
The charity, Myeloma UK, said no patient in the UK should die without having access to the drug.
A trial last year showed Velcade (bortezomib) could extend the life expectancy of a patient by an average of six months more than standard treatment. Treatment costs about £18,000 per patient.
The drug was approved for use in Scotland in 2004, where it is mainly used as a last resort.
The Daily Mail earlier reported that it had seen a leaked ruling, which said the drug was more clinically effective than chemotherapy but was not regarded as "cost effective".
Jacky Pickles, 44, one of three women with bone marrow cancer from Keighley in West Yorkshire, is campaigning to get the drug approved.
"If NICE is going to get away with not backing these drugs, then we will be stuck in the dark ages.
"Isn't three years of my life worth anything?"
Shadow health secretary Andrew Lansley said the NHS had become a "Scottish and a separate English health service".
Quality of life
NICE, which regulates primary care trusts in England and Wales, has come under repeated fire over its decisions not to fund drugs.
The guidance will be formally issued before the end of the year.
Objectors however can appeal against their decision.
Ms Sutcliffe, who led the appraisal for NICE, said the committee had considered comments received during consultation on an earlier draft and had not changed its conclusion.
"Although the drug is clinically effective compared with high dose dexamethasone, its cost-effectiveness has not been satisfactorily demonstrated and therefore further research is required."
A NICE spokesman added: "NICE has appraised 26 cancer treatments to date, and we have recommended 25 of them for use by the NHS."
A spokeswoman for Myeloma UK said the charity was taking legal advice over the ruling.
"This represents probably the single biggest setback in the history of the treatment of myeloma."
She said the entire myeloma community, including Myeloma UK and the other charities involved in the appraisal, were devastated.
"Velcade is a proven and licensed treatment and, quite simply, no myeloma patient in the UK should die without having access to it."