ATLANTA (CNNMoney.com) - Tykerb, an experimental new drug from GlaxoSmithKline, significantly slowed the spread of breast cancer in clinical trials, according to study results released Saturday.

The Glaxo (Research) treatment, a pill that is also called lapatinib, was tested on women with the aggressive HER2 breast cancer, which is present in about half of all cases.

Women who took Tykerb in conjunction with the Roche drug Xeloda cut in half the spread of breast cancer compared to those who took just Xeloda, said Dr. Charles Geyer, an independent researcher who led the study funded by GlaxoSmithKline, a Philadelphia-based drugmaker. Geyer is the director of breast cancer care at Allegheny General Hospital in Pittsburgh.

Breast cancer patients who took the Tykerb-Xeloda combination did not have cancer progression for an average of 36.9 weeks, compared to 19.7 weeks with just Xeloda, according to data presented at the American Society of Clinical Oncology annual conference in Atlanta on June 3.

During the course of the study, the breast cancer spread, sometimes leading to death, in 28 percent of the patients who took the drug combination, compared to 43 percent in those who took just Xeloda.

Due to the favorable results, the tests were halted early, said Geyer, the director of breast cancer care at Allegheny General Hospital in Pittsburgh. Studies are sometimes halted for ethical purposes - if a drug is shown to be effective, doctors may believe that patients in the study not taking it are being denied the best available care.

Geyer said Tykerb "should be considered a new standard of care for women with this disease" who meet the criteria shown in the test.

The study focused on 321 women who had not had success with the Genentech drug Herceptin, an injectable drug with sales of about $750 million last year.

Glaxo plans to file an application by the end of the year with the Food and Drug Administration to approve Tykerb. (see correction below)

Prior to today's release of data, Gbola Amusa of Sanford C. Bernstein projected that annual Tykerb sales could reach $1.5 billion by 2012, and could go higher.

Amusa said that Tykerb might be used in conjunction with Herceptin to treat all forms of HER2 breast cancer, and the drug could be key in transforming breast cancer from a deadly disease to a chronic one.

The drug industry for cancer, America's second-biggest killer behind heart disease, is growing rapidly. Cancer drug sales are expected to more than double over the five years, from $24 billion in 2004 to $55 billion in 2009, according to IMS Health, the healthcare research firm.

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CORRECTION: An earlier version of this story said that the Tykerb FDA application had already been filed.