GlaxoSmithKline (NYSE: GSK) stirred up cancer circles this month when the release of some clinical data of its melanoma treatment suggested that the experimental combination drug could work better than Roche‘s Zelboraf.

Roche subsidiary Genentech countered by saying that such comparisons were not valid because GSK’s study did not compare its drug candidate against the Roche drug.

That’s about to change.

GSK has started a phase 3 study of its drug in melanoma patients. Besides studying its combination drug against a placebo, GSK will also do a head-to-head study against the Roche product.

Zelboraf, also known a vemurafenib, is a BRAF inhibitor that works on patients who express mutations on the BRAF gene. The Roche product received priority review from the U.S. Food and Drug Administration and was considered a breakthrough cancer treatment when it received approval last year.

GSK’s dabrafenib is also a BRAF inhibitor. GSK’s phase 3 trial will study dabrafenib in combination with another compound, the MEK inhibitor trametinib. The British pharma, which has its U.S. headquarters in Research Triangle Park, North Carolina, believes that its combination therapy could give it an edge over other treatments.

“While recent clinical findings with BRAF inhibitors in melanoma have shown significant improvement over chemotherapy, eventually tumors become resistant to these inhibitors leading to disease relapse,” Dr. Rafael Amado, head of oncology R&D for GSK said in a statement. “Recent scientific advances have led us to the hypothesis that the combination of BRAF and MEK inhibitors may delay resistance.”

Results of an earlier dabrafenib/trametinib study are set to be highlighted this week at the annual meeting of the American Society of Clinical Oncologists. Those results, released earlier this month in a preview of the conference, showed that the progression-free survival for patients on the GSK combination treatment was 10.8 months, more than three months longer than progression-free survival shown in a vemurafenib study. But again, that study was not a head-to-head comparison. Roche plans to announce at the ASCO conference updated overall survival data for patients who have been treated with Zelboraf.