Pfizer's lung cancer drug Xalkori has shown positive results in reducing the size of tumors in lung cancer patients with a rare genetic mutation, an abnormality in the ROS1 gene.

Xalkori was approved to treat patients with a mutation of the ALK gene, along with a companion diagnostic test to identify those with the mutation, which accounts for about 4 percent of non-small cell lung cancers (NSCLC). About 1 to 2 percent of NSCLC patients are believed to be ROS1 positive.

According to the data presented at the European Society for Medical Oncology meeting, in the study of 50 non-small cell lung cancer patients with a rearrangement of the ROS1 gene, Xalkori treatment led to significant tumor shrinkage in 36 of them, or 72 percent, and halted tumor growth in 9 additional patients.

"This is the first definitive study to establish crizotinib's activity in a large group of patients with ROS1-positive lung cancer and confirms that ROS1 is a bona fide therapeutic target in those patients. The remissions induced by crizotinib in ROS1-positive patients are quite prolonged, and (treatment) resistance appears to emerge much later, on average, than what we have seen with other targeted therapies for lung cancer and melanoma," said Dr Alice Shaw, the study's lead investigator from the Massachusetts General Hospital Cancer Center, in a statement.

The study is published in the New England Journal of Medicine.