The true cost of making the new breast cancer drug Herceptin widely available on the NHS will be borne by patients who are denied other treatments, according to a team of doctors.
Hospitals in England and Wales have been told they should offer Herceptin to all suitable patients with early breast cancer.
But the new guidance from the National Institute for Health and Clinical Excellence (Nice) presents a financial headache for those holding the NHS purse strings.
To balance the books, providing the expensive drug may mean having to cut other effective treatments.
An illustration of what this may mean was described by cancer specialists at Norfolk and Norwich University Hospital NHS Trust.
Herceptin, which works for 20% to 25% of breast cancer patients with a particular defective gene, costs around £20,000 per year.
Doctors Ann Barrett, Tom Roques and Matthew Small calculated that in drug costs alone, they would have to find £1.9 million to treat 75 eligible patients with Herceptin.
Adding the cost of testing, monitoring, pharmacy preparation and drug administration pushed the figure up to £2.3 million.
The doctors wrote in the British Medical Journal: "These untreated patients will be people we know. We will be the ones to tell them they are not getting a treatment that has been proved to be effective, which costs relatively little, because it is not the 'treatment of the moment'.
"The real cost of Herceptin is in the other patients not treated, whether they are patients with cancer or those with other conditions. Nice gives no guidance on this issue."
