GlaxoSmithKline's new breast cancer drug Tykerb is to go head-to-head with Genentech's blockbuster Herceptin to see whether one is better or if patients should get both.
The U.S. National Cancer Institute said 8,000 participants in 50 countries would be given either Herceptin or Tykerb, or Herceptin followed by Tykerb, or the two treatments in combination.
Glaxo is providing financial support for the trial.
Both Herceptin and Tykerb, known generically as trastuzumab and lapatinib, have been approved for treating HER2-positive breast cancer, an aggressive form of the disease found in 20 to 30 percent of patients with a particular gene mutation.
The new study, expected to end in 2011, will provide oncologists with the first direct comparison of the drugs in the earliest, most treatable stages of cancer.
"It may be that using two treatments that work in different ways against HER2-positive breast cancer offers a complementary strategy that is more powerful than either drug alone," Dr Edith Perez of the Mayo Clinic in Jacksonville, Florida, who is leading the study, said in a statement.
HER2-positive breast cancer is caused by an excess of HER2 genes or by over-production of its protein, the HER2 cell surface receptor.
Herceptin consists of large antibodies that latch on to the portion of the HER2 protein on the outer surface of the cancer cell, while Tykerb acts by entering a cancer cell and binding to part of the protein lying beneath the cell surface.
The new study has two different designs depending on whether patients with stage I or stage II breast cancer have already been treated with chemotherapy. It will therefore compare four different regimens of targeted therapy administered over a 52-week period.
Herceptin is sold outside the United States by Genentech's partner Roche Holding.