The new drug Herceptin cuts the risk of tumors returning in women with early stage breast cancer by 50%, a US study has shown.
A second study in the New England Journal of Medicine showed Herceptin can also reduce cancer recurrence when combined with a chemotherapy drug.
A leading cancer expert called the studies' findings "stunning".
But they will increase pressure on regulators to make Herceptin available for early as well as advanced cancers.
Herceptin, which also has the generic name traztuzumab, targets a protein called HER2, which appears to be over-abundant in some women's breast cancers.
An estimated fifth of breast cancer cases - around 10,000 women in the UK - are HER2 positive.
Roche, which makes Herceptin, has to submit an application to European regulators before the drug can be licensed for use in early-stage disease.
The National Institute for Health and Clinical Excellence then has to give its approval for the drug to be prescribed on the NHS, reports BBC.
Breast cancer charities were exultant yesterday. Jeremy Hughes, chief executive of Breakthrough Breast Cancer said: "This is one of the biggest breakthroughs in breast cancer treatment. It is vital this drug, which is set to save about 1,000 women's lives a year, is made available on the NHS without delay."
The results helped boost sales for Roche, the Swiss-based pharmaceutical company, which reported third quarter profits up 20 per cent yesterday. Roche also makes Tamiflu, the drug being stockpiled by countries around the world as a defence against the threatened pandemic of avian flu.
The research on Herceptin triggered a worldwide demand for the drug even before it was licensed for early breast cancer (it is currently licensed only for advanced breast cancer that has spread to other organs). Last month, a nurse, Barbara Clark, shamed Somerset Primary Care Trust into providing the drug, which costs around Ј20,000 for a year's treatment, after threatening to take her case to the European Court of Human Rights.
Following Ms Clark's victory, Patricia Hewitt, the Health Secretary, pledged Herceptin would be available to all newly diagnosed patients with breast cancer who were suitable for it. Existing patients would have to apply for funding to their health authorities on a case by case basis the health department said, informs Independent.