Lack of ROS1 gene rearrangement in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most aggressive type of brain tumor, and the prognosis remains poor. Rearrangement of ROS1 gene, which was shown to have an oncogenic potential, was previously discovered in GBM cell lines. In this pilot study, we aimed to identify the incidence of ROS1 rearrangement in GBM patient tissues to explore novel biomarkers for therapeutic strategy. Formalin-fixed and paraffin-embedded (FFPE) tissue sections from 109 patients with GBM were screened for ROS1 rearrangement by anti-ROS immunohistochemistry (IHC) and ROS1 break-apart fluorescent in situ hybridization (FISH) assays. O⁶-methylguanine-DNA methyltransferase (MGMT) gene promoter methylation and Isocitrate dehydrogenase 1 (IDH1) mutation status were also assessed. All samples were interpreted by two experienced pathologists who were blinded to the clinical data. A total of 109 samples were collected and all samples were examined for ROS1 rearrangement by IHC and FISH assays, and none was found to harbor ROS1 rearrangement. MGMT gene methylation was found in 42 (39.2%) cases, and IDH1 mutation was found in 6 (5.5%) cases. In this study, ROS1 rearrangement was not identified in GBM patients, and thus it is difficult to classify ROS1 rearrangement as a novel molecular subset in GBM patients for now.