Roche says a late-stage trial of its experimental antibody-drug conjugate T-DM1 helped women with previously treated HER2-positive metastatic breast cancer live significantly longer than women who received the standard of care, a combination of drugs from GlaxoSmithKline and Roche’s own Genentech.

Hal Barron, Roche’s Chief Medical Officer and Head of Global Product Development, says he’s “extremely pleased” with the new data, reported at the European Society for Medical Oncology Congress in Vienna.

Results of the international randomized, open-label EMILIA study showed that women taking T-DM1 survived a median of 5.8 months longer than those who received a combination of GlaxoSmithKline’s Tykerb and Genentech’s Xeloda. Median overall survival for T-DM1 patients in the trial was 30.9 months versus 25.1 months for trial patients taking Tykerb and Xeloda.

The study followed 991 people with HER2-positive locally advanced or metastatic breast cancer who had previously been treated with Herceptin and a taxane chemotherapy. The study turned up no new safety signals, and following release of the new overall survival results, women in the control arm of the study are now being offered the option to receive T-DM1.

Each year about 1.4 million new cases of breast cancer are diagnosed worldwide. About 15 percent to 20 percent of the women diagnosed with the disease have the form for which Roche is testing the drug. Breast cancer is the most common cancer in women in the United States and is the second most common cause of cancer death in women.

T-DM1 combines trastuzumab, the active ingredient in Roche’s breast cancer drug Herceptin, with a targeted antibody payload technology Genentech licensed from ImmunoGen. The combination of the monoclonal antibody with a powerful cancer drug delivers the therapy directly to the tumor cells, bypassing healthy cells.

Roche is seeking regulatory approval for T-DM1 from the U.S. Food and Drug Administration and the European Medicines Agency for use in women with HER2-positive, unresectable, locally advanced or metastatic breast cancer.