Zhao J, et al. - The driver mutation and clinicopathologic features of 26 discordant non–small cell lung cancer cases [ROS1 immunohistochemistry (IHC)-positive, but fluorescent in situ hybridization (FISH)-negative] were determined to distinguish ROS1-rearranged cases. Distinct clinical and morphologic features were demonstrated in ROS1-discordant patients, often harboring another oncogenic driver alteration compared with ROS1-rearranged cases. The use of optimized screening criteria raises the specificity of the ROS1 antibody.