An experimental drug kept breast cancer in check twice as long as conventional treatment among women whose aggressive tumors had already been treated with Herceptin.

The drug, called Tykerb or lapatinib, along with the chemotherapy agent capecitabine, also known as Xeloda, stopped cancer progression for an average of 8¹/₂ months, while capecitabine alone worked for only about half that time.

Counting Herceptin as the first, Tykerb "is a second drug that has a very important impact on controlling these aggressive breast cancers," said lead investigator Dr. Charles Geyer, director of breast medical oncology at Allegheny General Hospital.

Early findings from the international trial were announced today in Atlanta at the annual meeting of the American Society of Clinical Oncology.

The study included more than 300 women with late-stage breast cancers bearing the HER-2 marker and who had already been treated with Herceptin, also called trastuzumab. The patients were randomly assigned to take capecitabine alone or in combination with Tykerb.

About 20 to 25 percent of all breast cancers are HER-2 positive, and they tend to be more aggressive and more likely to recur, Dr. Geyer said. Herceptin blocks HER-2 receptors on the cell surfaces, while Tykerb targets the portion of the receptor that is within the cell.

When the trial began, the researchers expected to monitor more than 500 patients to see whether Tykerb worked. But it made such an obvious difference that the study ended early.

The study showed that adding Tykerb "essentially doubled the period of time the cancers seemed to be controlled" compared to chemotherapy alone, Dr. Geyer explained. He added that it's unusual to see that much of an effect in late-stage disease.

Also, women who took Tykerb were less likely to have cancer spread into the brain. Side effects were similar between the treatment groups, although the Tykerb patients were more likely to have mild to moderate diarrhea or a rash.

"It seems like a small number, [but] four months in people with advanced disease is really a huge difference," said Dr. Victor Vogel, a breast cancer expert at Magee-Womens Hospital. "It's very encouraging data."

More studies need to be done to determine whether Tykerb could be used in the treatment of earlier stages of breast cancer, or as a first-line therapy for metastatic disease, said Dr. Vogel, who was not a member of the research team.

"These are all a whole host of research questions that are generated by this kind of positive result," Dr. Geyer said. "It's exciting, really."

Federal authorities must approve Tykerb before doctors can use it. The drug might become available sooner under a compassionate use protocol for breast cancer patients who aren't being helped by Herceptin, Dr. Geyer said.

GlaxoSmithKline, the maker of Tykerb, funded the study.