ROS1 Fusions Rarely Overlap with Other Oncogenic Drivers in Non–Small Cell Lung Cancer

IntroductionChromosomal rearrangements involving the gene ROS1 define a distinct molecular subset of NSCLCs with sensitivity to ROS1 inhibitors. Recent reports have suggested a significant overlap between ROS1 fusions and other oncogenic driver alterations, including mutations in EGFR and KRAS.MethodsWe identified patients at our institution with ROS1-rearranged NSCLC who had undergone testing for genetic alterations in additional oncogenes, including EGFR, KRAS, and anaplastic lymphoma receptor tyrosine kinase gene (ALK). Clinicopathologic features and genetic testing results were reviewed. We also examined a separate database of ROS1-rearranged NSCLCs identified through the commercial FoundationOne assay (Foundation Medicine, Cambridge, MA).ResultsAmong 62 patients with ROS1-rearranged NSCLC evaluated at our institution, none harbored concurrent ALK fusions (0%) or EGFR activating mutations (0%). KRAS mutations were detected in two cases (3.2%), one of which harbored a concurrent noncanonical KRAS I24N mutation of unknown biological significance. In a separate ROS1 fluorescence in situ hybridization–positive case, targeted sequencing failed to confirm a ROS1 fusion but instead identified a KRAS G13D mutation. No concurrent mutations in B-Raf proto-oncogene, serine/threonine kinase gene (BRAF), erb-b2 receptor tyrosine kinase 2 gene (ERBB2), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha gene (PIK3CA), AKT/serine threonine kinase 1 gene (AKT1), or mitogen-activated protein kinase kinase 1 gene (MAP2K1) were detected. Analysis of an independent data set of 166 ROS1-rearranged NSCLCs identified by FoundationOne demonstrated rare cases with co-occurring driver mutations in EGFR (one of 166) and KRAS (three of 166) and no cases with co-occurring ROS1 and ALK rearrangements.ConclusionsROS1 rearrangements rarely overlap with alterations in EGFR, KRAS, ALK, or other targetable oncogenes in NSCLC.