GlaxoSmithKline

(GSK) - Get Report

plans to pursue regulatory approval of a treatment for advanced breast cancer later this year after seeing strong results in a late-stage clinical trial.

The company said Monday that the test results were so good that an independent data-monitoring committee recommended that GlaxoSmithKline halt enrollment in an ongoing trial comparing a chemotherapy pill, Xeloda, with a combination treatment of Xeloda and the experimental drug Tykerb. Switzerland's

Roche

makes Xeloda.

GlaxoSmithKline had expected to seek regulatory approval for Tykerb in late 2006 or the first half of 2007. Now, it said it will file applications with the Food and Drug Administration and its European Union counterpart during the second half of this year.

"We are extremely encouraged by these data," said Dr. Paolo Paoletti, senior vice president of the company's oncology medicine development center.

Glaxo's stock gained 53 cents, or 1%, to close at $52.84.

Tykerb was tested as a treatment for a certain type of breast cancer that had advanced or spread to other organs and that was triggered by the cancer gene called ErbB2. The combination Tykerb-Xeloda treatment was given to women whose breast cancer had continued after having been treated with Herceptin, a

Genentech

(DNA)

drug, or other cancer therapies.

The test was stopped after a preliminary analysis of 321 patients yielded "statistically significant results," beating the test goal. All women currently enrolled in the trial will continue to be followed, and those who are receiving Xeloda alone will be offered the option of switching to the combination therapy.

The study wanted to see if the Xeloda-Tykerb combination could slow the return of tumors that had been treated. To be successful, the combination had to cause at least a 50% increase in what researchers call "time to disease progression" vs. Xeloda alone. Using this terminology, a greater increase in time to disease progression means a longer the delay in the tumor's return.