HGG-23. The presence ofROS1 fusions are not limited only to infantile hemispheric glioma.

INTRODUCTION: Diffuse pediatric-type high-grade gliomas are diffuse gliomas with histological features of malignancy, typically occurring in children, and infants. For these tumors, precise classification, identification of prognostic and predictive factors requires molecular analysis. The ROS proto-oncogene 1 (ROS1) gene encodes a receptor tyrosine kinase that is involved in chromosomal rearrangements in numerous malignancies, and may be an attractive therapeutic target, since specific inhibitors have been approved for several neoplasms. Molecular evaluation including detection of ROS1 fusions in pediatric gliomas are not included in standard diagnostic tests so far, therefore data on its significance is still limited. We present two cases of pediatric ROS1 fusion-positive brain tumors. METHODS AND RESULTS: The patient no.1 was 1 year old boy with disseminated brain lesions. Histopathological examination displayed the presence of a neoplasm, which was composed of round and spindle-shaped cells with palisading necrosis, mitotic activity, and microvascular proliferation. The patient no.2 is 9 years old girl with tumor located in left frontal lobe. Microscopically, the neoplasm revealed the presence of oligodenroglial-like component with microvascular proliferation, and high mitotic activity. Targeted gene sequencing panel - Ampliseq Childhood Cancer Panel for Illumina was used to detect diagnostic and targetable gene fusions. In both of patients ROS1:GOPC gene fusions were detect. Identified fusions allowed to established diagnosis - infant-type hemispheric glioma with ROS1 fusion (patient no 1) and - diffuse pediatric-type high grade glioma with ROS1 fusion (patient no 2). CONCLUSIONS: Our results indicate, that the presence of ROS1 fusions are not limited to the infant-type hemispheric gliomas only and may play a role in other glioma entities. It may be worth to include this biomarker in the diagnostic panel of pediatric brain tumors to establish a more precise diagnosis and a potential therapeutic target. Funded by National Science Centre, Poland (2016/23/B/NZ2/03064).