Pfizer’s lung-cancer treatment Xalkori received a Breakthrough Therapy designation from the FDA for patients with ROS1-positive non-small cell lung cancer.

Xalkori is currently approved for use in patients with metastatic NSCLC, whose tumors are anaplastic lymphoma kinase-positive.

Some mutations of ROS1 have been identified as a possible “driver” mutation in non-small cell lung cancer. A 2012 study in the Journal of Clinical Oncology found that roughly 2% of lung tumors contain these ROS1 fusions, or mutations.

Xalkori generated sales of $438 million in 2014, up from $282 million in the same period for 2013.