ROS1 and neoplasm: Of note, ROS1 expression, typically focal, can be found in up to one-third of tumours without underlying ROS1 rearrangements, but with other genomic alterations (e.g., mutations of EGFR, kirsten rat sarcoma virus [KRAS], BRAF or human epidermal growth factor receptor 2 [HER2], and ALK rearrangements) [28, 29].