ROS1 rearrangement and response to crizotinib in Stage IV non-small cell lung cancer

Background: The frequency of ROS1 rearrangement in non-small cell lung cancers has been reported from 1.6% to 2.3%. Materials and Methods: We examined 105 lung adenocarcinoma patients for ROS1 rearrangement which were negative for EGFR and anaplastic lymphoma kinase. Clinical characteristics of ROS1 rearranged patients and their responses to crizotinib therapy were studied. Results: Of the 105 patients, three cases were positive for ROS1 rearrangement by fluorescence in situ hybridization analysis. All of them showed heterogeneous pattern. All the 3 ROS1-positive patients were females in their forties and started on crizotinib. All of them responded to treatment. One of them developed resistance after 3 months. Another one showed marked systemic response but central nervous system lesions progressed. The third case is doing well till date with inactive lesions on positron emission tomography scan. Conclusions: The frequency of ROS1 rearrangement is low in non-small cell lung carcinoma, but their diagnosis offers patients an opportunity to receive highly effective targeted therapies