Test Details: Activating mutations in EGFR are present in approximately 10-12% of Non small cell lung carcinoma (NSCLC), most of which predict a good response to treatment with EGFR inhibitors such as gefitinib and erlotinib. Exceptions are insertion mutations in exon 20 and the T790M substitution, which confer resistance to these drugs. ALK gene rearrangements are present in approximately 5% of NSCLC, the most common being EML4-ALK fusion. Activation of ALK kinase through these gene fusions can be inhibited by ALK inhibitors such as crizotinib. Gene fusions involving ROS1 are present in 1-2% of NSCLC. ROS1 gene fusions activate ROS kinase which is sensitive to crizotinib.