LOS ANGELES A combination of two experimental antibody drugs shrank tumors in 40 percent of women with advanced breast cancer whose tumors generate a protein called HER2, according to interim results from a small, early-stage trial.
The Phase Ib/II trial evaluated a combination including T-DM1 -- an "armed antibody" that ties Roche Holding AG's blockbuster drug Herceptin to a toxic chemotherapy compound from ImmunoGen Inc.
The other half of the therapy was Roche's pertuzumab, an antibody designed to stop HER2 from interacting with other members of the same protein family.
Herceptin is designed to block the function of HER2, a protein produced by a specific gene with cancer-causing potential that is generated by 25 percent to 30 percent of breast cancers.
Preliminary results from the 67-patient trial showed that the two experimental drugs shrank tumors in nine of 23 women whose cancer had worsened after a median of eight prior treatments.
The women had been previously treated with drugs including Herceptin, also known as tratuzumab, and GlaxoSmithKline PLC's Tykerb, also known as lapatinib.
The trial results were posted on Thursday as part of the program for the upcoming annual meeting of the American Society of Clinical Oncology.
A spokeswoman for Roche's Genentech unit said updated trial results would be presented at the conference in early June.
Researchers said the trial suggested that T-DM1 plus pertuzumab, once known as Omnitarg, did not increase the serious side affects previously reported for T-DM1 alone.
The most common adverse events with the combination were nausea, fatigue, decreased appetite, impaired taste and diarrhea.
One patient had a serious adverse event involving diarrhea, fatigue, nausea and vomiting, and another patient had serious problem with labored breathing. One patient died from pneumonia following disease progression.
Roche plans to file for accelerated U.S. regulatory approval of TDM-1, based on a Phase II study in heavily pretreated patients, in the second half of this year.
Results from a Phase III trial of the armed antibody as a second-line treatment for breast cancer patients are expected in 2012.
(Reporting by Deena Beasley; Editing by Steve Orlofsky)