Moves to block a new breast cancer drug which extends women's lives by almost six months have been described as a "major blow".
Clinical trial results have shown that women on Kadcyla survived 30.9 months compared with 25.1 months on similar treatments.
However, the National Institute for Health and Care Excellence (Nice) said in its draft guidance the drug is not effective enough to justify the price the NHS is being asked to pay.
It is estimated that Kadcyla, manufactured by Roche, will cost around £90,000 per patient.
Nice chief executive Sir Andrew Dillon said: "We had hoped that Roche would have recognised the challenge the NHS faces in managing the adoption of expensive new treatments by reducing the cost of Kadcyla to the NHS.
"We apply as much flexibility as we can in approving new treatments, but the reality is that given its price and what it offers to patients, it will displace more health benefit which the NHS could achieve in other ways than it will offer to patients with breast cancer."
Professor Paul Ellis, a consultant oncologist at King's College, London and lead triallist for the drug in the UK, said: "Kadcyla represents a significant advance in HER2-positive breast cancer, so for Nice to issue negative preliminary guidance is a huge blow.
Jayson Dallas, general manager of Roche Products Limited, said: "Roche is extremely disappointed that Nice has failed to safeguard the interests of patients with this advanced stage of aggressive disease."
Kadcyla, which is only suitable for patients with the defective Her2 gene, is designed to penetrate cancer cells and destroy them from within and, because its action is so precise, a normally toxic form of chemotherapy can be used.
It is currently given to breast cancer patients who have failed on conventional treatment with Herceptin and chemotherapy.
The decision by Nice is now up for public consultation and during this time patients will be able to apply to their local NHS and to the Cancer Drugs Fund (CDF) for the drug.