Just weeks after announcing a fresh batch of promising Phase III data, the FDA has handed Genentech and its biotech partner Exelixis ($EXEL) an approval to market cobimetinib in combination with Zelboraf among a genetically defined group of melanoma patients.

The drug will be sold as Cotellic, a new weapon that can be used to fight drug-resistant skin cancer.

The MEK inhibitor combined with Zelboraf (vemurafenib) — a BRAF inhibitor — has posted consistently promising data for melanoma patients who test positive for a BRAF V600 E or V600K mutation.

In May, Exelixis announced a progression-free survival rate of 12.3 months for their combo, compared with 7.2 months for Zelboraf alone. At least one analyst had forecast peak potential sales at $790 million.

Cobimetinib's success in the clinic has helped Exelixis mark a turnaround from the failure of cabozantinib in prostate cancer. That flop last year triggered a major reorganization with 70% of the staff laid off.

Exelixis exercised its U.S. copromotion rights for cobimetinib two years ago and has said it is prepared to field up to 25% of the sales force for the therapy. Roche, meanwhile, is counting another successful program at its big Genentech subsidiary. The company noted today that this OK marks the pharma giant's seventh new drug approval in five years.

"As we continue to advance our knowledge of tumor biology, we have learned that cancer cells have a remarkable ability to adapt and become resistant to targeted therapies," said Dr. Richard Pazdur, director of the Office of Hematology and Oncology Products in the US Food and Drug Administration's Center for Drug Evaluation and Research. "Combining two or more treatments addressing different cancer-causing targets may help to address this challenge. Today's approval provides a new targeted treatment that, when added to vemurafenib, demonstrates greater benefit than vemurafenib alone in patients with BRAF mutation-positive melanoma."

Here's the FDA's release.