Almost 3,000 people are diagnosed with chronic lymphocytic leukaemia (CLL) in the UK each year, but a drug that could treat the condition will not be made available on the NHS, according to a ruling by a health watchdog.
Health officials from the National Institute for Health and Care Excellence (Nice) have said the new leukaemia drug, obinutuzumab, should not be used widely by the NHS.
In new draft guidance the NHS authority said that "uncertainties" over manufacturer Roche's data means it it unable to recommend the drug.
Earlier this year, charity Leukaemia and Lymphoma Research said obinutuzumab, also known as Gazyvaro, could give patients "effective, life-prolonging treatment".
The drug appears to be "more effective" than another monoclonal antibody - a medication which harnesses the body's own immune system to target cancer cells - which is currently used alongside chemotherapy to treat CLL, the blood cancer charity said.
In May, Roche said that the drug can "reduce the risk of cancer worsening or death by up to 86%" when used with chemotherapy compared to just having chemotherapy alone for patients with CLL.
The pharmaceutical company said that 22% of patients who took the drug alongside chemotherapy during clinical trials were "disease free" after treatment.
But in its preliminary guidance Nice has said that it "cannot be confident" that recommending the drug is an effective use of NHS money.
Sir Andrew Dillon, Nice chief executive, said: "Chronic lymphocytic leukaemia is the most common form of leukaemia in the UK, with around 2,700 people being diagnosed with the condition each year.
"Half of the people who need treatment for their condition are not able to use the standard first-line therapy. Nice recommended alternative treatments are already available.
"Although obinutuzumab is a clinically effective treatment, there were too many uncertainties in the company's submission and we cannot be confident that it is an effective use of NHS resources.
"It is disappointing that we are not able to add this to the range of treatments already available. However, with limited resources we need to ensure that each treatment we recommend gives patients not only the best care but is also of the best value to the NHS."
Professor Chris Bunce, research director at Leukaemia and Lymphoma Research, said: "This decision by Nice is disappointing.
"They recognise that obinutuzumab is an effective treatment but state that 'too many uncertainties in the company's submission' prevented them from being confident that the drug would be a valuable use of NHS resources.
"The nature of this statement brings into question whether the mechanisms for Nice to work with drug companies prior to submissions for final assessment are appropriate.
"The role of Nice is challenging but it is imperative that the decisions they make are driven not just by cost but equally by patient need. For the benefit of patients it is important that Nice is a body that drug companies can work with and not just a hurdle they have to surpass."