However, crizotinib was also found to be a potent inhibitor of the Echinoderm Microtubule associated protein-Like 4-Anablastic Lymphoma Kinase (EML4-ALK) fusion protein and the ROS proto-oncogene 1 tyrosine-protein kinase (ROS1) which led to its U.S. Food and Drug Administration (FDA) approval for treatment of ALK-positive non-small cell lung cancer (NSCLC) in 2011 [13] and ROS1-postive NSCLC in 2016 [14]. The gene discussed is ALK; the disease is non-small cell lung carcinoma.