Pfizer's Xalkori has become the first drug to be approved in the US for ROS1-positive non-small cell lung cancer (NSCLC), a rare and treatment-resistant form of the disease.
ROS1-positive cancers are quite infrequent but there is no standard treatment available and patients are in desperate need of new therapeutic options. For that reason Xalkori was granted both breakthrough and priority review status by the FDA.
Xalkori (crizotinib) - which combines inhibition of ALK, ROS1 and MET - was first approved for the treatment of ALK-positive NSCLC in 2012 and is among Pfizer's fastest-growing drugs, rising 20% to $488m last year.
Richard Pazdur, director of the Office of Hematology and Oncology Products at the FDA, said the approval "will provide a valuable treatment option for patients with the rare and difficult-to-treat ROS1 gene mutation by giving healthcare practitioners a more personalised way of targeting ROS1-positive NSCLC".
ROS1 mutations are seen in approximately 1% of the 1.5m new cases of NSCLC diagnosed each year around the world and share common features with ALK mutations even though they are rarely encountered in the same tumour.
ROS1 rearrangements occur when the ROS1 gene attaches to another gene and changes the way each gene normally functions, which can contribute to cancer-cell growth.
The new approval comes on the back of a phase I study in 50 patients with ROS1-positive NSCLC who were treated with oral Xalkori twice daily. Treatment with Pfizer's drug was associated with an overall response rate of 66%, including one complete response and 32 partial responses, with the effect lasting a median of around 18 months.
Use of Xalkori in ALK-positive NSCLC is determined by an FDA-approved diagnostic test and for the moment there is no equivalent for the ROS1-positive patient population. Pfizer says it is working on the development of a companion diagnostic for the new indication.
The company has also submitted the clinical data in ROS1-positive NSCLC to the European Medicines Agency (EMA). Xalkori was approved as a first-line therapy for ALK-positive NSCLC last December.
Pfizer's drug - which is partnered with Merck KGaA - was the only ALK inhibitor on the market until last year when it was joined by Novartis' Zykadia (ceritinib) and Roche's Alecensa (alectinib), which have both been approved for use in ALK-positive NSCLC patients who have previously been treated with Xalkori.