A anti-cancer drug already used for lung cancer has won expanded approval from the U.S. Food and Drug Administration to treat another rare form of the disease.

The drug Xalkori (crizotinib) is already used to treat some forms of lung cancer, and now the agency also has expanded it for use in tumors that test positive for a genetic mutation known as ROS-1 that is found in non small cell lung cancer (NSCLC), which is the most common form of the often-deadly disease, the FDA said. 

"Lung cancer is difficult to treat, in part because patients have different mutations, some of which are rare. The expanded use of Xalkori will provide a valuable treatment option for patients with the rare and difficult-to-treat ROS-1 gene mutation,” says Dr. Richard Pazdur, director of the agency’s Office of Hematology and Oncology Products division.

By blocking the activity of the ROS-1 protein in tumors that have ROS-1 gene alterations, crizotinib may prevent NSCLC from growing and spreading, the FDA says.

The FDA evaluated the drug in 50 patients and found that 66 percent of them experienced complete or partial shrinkage of their tumors, an effect that lasted an average of 18.3 months, the FDA said.

These types of gene alterations are present in roughly 1 percent of patients with NSCLC.