A breast cancer drug that has been shown to almost double the eradication of tumours has been rejected for use on the NHS.
In draft guidance, the National Institute for Health and Care Excellence (Nice) said it was uncertain how the effects of Perjeta (also called pertuzumab) seen in clinical trials would translate into long-term benefit for patients.
The news will come as a blow to some campaigners as there has been much excitement about the potential of Perjeta.
The drug, manufactured by Roche, is for use in women with HER2-positive breast cancer prior to surgery.
About 15% of women with early-stage breast cancer have HER2 positive cancer.
According to Roche, the medicine has the potential to help more than 1,800 patients in the UK.
In clinical trials, Roche said Perjeta almost doubled the number of women whose tumours were eradicated compared with current treatment.
Additional data showed that patients were 40% more likely to be disease-free after three years.
Perjeta works by targeting the HER2 protein, which is found on the surface of some cancer cells. It stops HER2 joining to other HER proteins so the cell does not receive messages telling it to grow.
Perjeta is licensed for use in combination with the current treatment Herceptin (trastuzumab) and chemotherapy for earlier-stage cancer.
In the new guidance for England, Nice said there was a lack of long-term evidence comparing Perjeta with other treatments used before breast cancer surgery.
It looked at the drug for HER2 breast cancer that was locally advanced, inflammatory, or early-stage and at high risk of coming back.
While there was evidence that the combination of drugs was more successful at getting rid of cancer in the breast and lymph nodes before surgery, Nice said it was "very uncertain" about the extent to which this would cut the chances of cancer coming back and longer survival.
Perjeta costs £2,395 per 420mg vial (excluding VAT). The total cost of treatment ranges from £7,185 (for three cycles of treatment) to £16,765 (for six cycles of treatment).
Sir Andrew Dillon, Nice chief executive, said: "In order to be able to recommend pertuzumab as an addition to trastuzumab and chemotherapy, the committee needed to have more evidence of its long-term clinical benefits, particularly its impact on overall survival.
"On the basis of the evidence presented, the committee was very unsure about the extent of these benefits."
Anyone already on the drug will be able to continue receiving it.
Baroness Delyth Morgan, chief executive at Breast Cancer Now, said: "This is a disappointing but not unexpected decision. Perjeta before surgery has shown some promising early results, and could benefit up to 15% of breast cancer patients, but the clinical evidence is still insufficient.
"We sincerely hope this is what the new Cancer Drugs Fund and Nice's 'maybe' option will be used for: to gather further data and allow patients access while this evidence is collected.
"Our major concern remains that the Nice appraisal process remains too inflexible to cope with the complexities of modern cancer drugs. We need the Prime Minister to intervene and review the appraisal system for new drugs, which has still not been significantly updated since 1999."
Samia al Qadhi, chief executive of Breast Cancer Care, said: "This is bitterly disappointing as pertuzumab (Perjeta) has the exciting potential to shrink tumours for some breast cancer patients before surgery.
"All breast cancer patients deserve the very best treatment and it is frustrating when access to any drug which could help them is denied.
"However, we still need to see further evidence of the long-term impact this drug can have on survival rates. We look forward to seeing the results of longer term studies."