As per established therapeutic protocols, it is mandatory for all patients diagnosed with metastatic non-small cell lung cancer (NSCLC) to undergo immunohistochemistry (IHC) testing to determine PD-L1 expression and the presence of other oncogenic driver mutations, including EGFR, ALK, ROS-1, and BRAF, prior to the initiation of treatment regimen (25). The gene discussed is ROS1; the disease is non-small cell lung carcinoma.