Adenocarcinoma cells were detected in the pericardial fluid, and ROS1 gene rearrangement was found on examination of the cell block prepared from the same pericardial effusion using next-generation sequencing (Oncomine Comprehensive Assay v3; Thermo Fisher Scientific, Waltham, MA) (Figure 4). The gene discussed is ROS1; the disease is adenocarcinoma.