ROS1 is a receptor tyrosine kinase of insulin receptor family. Chromosomal rearrangements involving the ROS1 receptor tyrosine kinase gene occur in a subset of non–small-cell lung cancer (NSCLC). The ROS1 fusion partners include SLC34A2, CD74, SDC4, EZR etc. These fusions lead to constitutive kinase activity and activation of downstream pathways, such as JAK/STAT, PI3K/AKT, RAS/MAPK etc., leading to carcinogenesis. It has been reported that the presence of the ROS1 rearrangement is correlated with the efficacy of TKI therapy.Based on analysis of tumor messenger RNA, ROS1 gene fusions can be detected by real-time PCR method.