The ROS1 gene encodes a receptor protein-tyrosine kinase that consists of 2347 amino acid residues making it the largest member of this enzyme-receptor family. The ROS1 fusion partners include CD74, CCKC6, EZR, FIG, KDELR2, LRIG3, MSN, SDC4, SLC34A2, TMEM106B, TMP, and TPD-52L1. Physiological ROS1 is closely related to the ALK, LTK, and insulin receptor protein-tyrosine kinases[1]. Moreover, several of the ROS1 fusion proteins are implicated in the pathogenesis of a very small proportion of other cancers including glioblastoma, angiosarcoma, and cholangiocarcinoma as well as ovarian, gastric, and colorectal carcinomas. The occurrence of oncogenic ROS1 fusion proteins, particularly in non-small cell lung cancer, has fostered considerable interest in the development of ROS1 inhibitors[2].