The drug is already used for advanced cancer
All women in England with early stage breast cancer are to be tested to see if they could benefit from the drug Herceptin, ministers have announced.
The drug is currently licensed only for use in women with advanced breast cancer.
But it is also thought to be effective at treating the early stages.
Testing now should mean women in England who could benefit can receive the drug as soon as the licence is extended, probably next year.
Herceptin has the potential to save many women's lives and I want to see it in widespread use on the NHS
Health Secretary Patricia Hewitt
CPS:LINK HREF="" ID="4312476" STYLE="rightarrow">Testing shortfall
Health Secretary Patricia Hewitt has already ordered the National Institute for Health and Clinical Excellence (NICE), the drugs watchdog, to fast track its assessment of the wider use of Herceptin.
That process can begin now, but can only be completed once the drug's licence has been extended - the application for which will be submitted in February next year.
Herceptin targets a protein called HER2, which appears to be over-abundant in some women's breast cancers.
An estimated fifth of breast cancer cases are HER2 positive.
Campaigners, including the Fighting for Herceptin group who last month presented a petition of 34,000 signatures to Downing Street, are calling for immediate wider access to the drug.
Primary care trusts (PCTs) can currently fund Herceptin treatment for women with early stage breast cancer, if they so wish, but campaigners say lack of funds and official approval mean that many women who could benefit are being denied the drug.
On Tuesday, former nurse Barbara Clark was told she could have Herceptin on the NHS after taking her case to her local primary care trust.
Mrs Clark, who has early stage breast cancer, had been told she would have to pay privately for the drug.
She welcomed the government's announcement as "absolutely marvellous".
"Patricia Hewitt has been very go-ahead in what she has done."
Under the government's plan, testing for the HER-2 receptor would take place when women undergo breast cancer surgery.
It targets the HER2 protein, which can fuel the growth of breast tumours
Herceptin prevents this process happening
Around a fifth of breast cancers are HER2 positive
It is currently licensed for use in women with advanced breast cancer - where the disease has spread within the breast or to another organ
Early stage breast cancer refers to the first occurrence of the disease
The cost for one year's treatment with Herceptin is £19,500
If chemotherapy and/or radiotherapy, which take some months, do not eradicate the cancer, it is at this stage women would be given Herceptin.
The government says this timescale means that, by introducing routine HER-2 testing now, women would be able to benefit as soon as Herceptin is licensed for use on the NHS.
The company which makes the drug, Roche, says the application for widening the use of Herceptin cannot be made any sooner than February because data from independent research has to be evaluated before it can be submitted.
Cancer Tzar Professor Mike Richards has been asked to ensure that the NHS has the facilities needed to test all women with early stage breast cancer.
Ms Hewitt said: "Herceptin has the potential to save many women's lives and I want to see it in widespread use on the NHS.
"I want the licence for Herceptin to be granted as quickly as possible, without compromising people's safety, and to be available within weeks of the licence being given."
She added: "I share the huge frustration of many women about the delays in getting Herceptin licensed.
"I am determined to take action, and this represents a major step forward in our fight against cancer."
Ms Hewitt pledged funding would be found to provide Herceptin to women who could benefit from it.
Professor John Toy of Cancer Research UK said: "This shows that 'patient power' can move government to take pro-active decisions."
But he added: "Patients need to understand that the drug is not expected to be licensed until July 2006 at the earliest. A process to make the drug available as quickly as possible after licensing is especially important given this delay."
Joanne Rule, Chief Executive of CancerBACUP, said: "This is extremely good news that all women with breast cancer will be tested to see if they are suitable for treatment with Herceptin.
"An automatic right to a HER2 test will allow women to know what their treatment options are so this is an important step in the right direction."
But she added: "We are still, concerned, however, that Herceptin will not be available for women with early breast cancer until 2006.
"The Department of Health must urgently consider making it available to all women who can benefit."
Emma Taggart, Breakthrough Breast Cancer's Policy and Campaign's Director, welcomed the announcement of routine testing.
"Without this service, moves to fast track both the licensing and NICE approval process are redundant. We look forward to seeing the detail of the plans to understand exactly how it will be achieved."
Steve Webb, Liberal Democrat health spokesman, said: "The government must ensure that local trusts, who hold the purse strings of the NHS, have sufficient funds to fulfil the promises ministers have made today."
Shadow Health Secretary Andrew Lansley said: "NICE should be in charge of implementing any guidelines, not the government."