Abstract BACKGROUND: Fibroblast growth factor receptor (FGFR) 4 is reportedly expressed in several cancer types, and is a high-affinity transmembrane receptor for FGF2 which is expressed human astrocytomas. However, the expression of FGFR4 across gliomas of different grades and histologies has not been extensively investigated. METHODS: We performed immunohistochemistry (IHC) of 178 grade II-IV human gliomas from our tumor bank, including 117 GBMs and 61 lower grade gliomas of astrocytic and oligodendroglial lineage. The samples were scored (0-2) separately for staining intensity and fraction of area that was stained and whether staining was predominantly cytoplasmic or nuclear. This scoring was performed separately for tissue from tumor center and periphery, as well as in tumor areas around pseudopalisading (PP) and large necroses. We also performed western blot analysis (n = 22) and real-time qPCR (n = 37). On one tumor sample we performed FISH for EGFR (red)/Centromere chromosome 7 (green), combined with immunofluorescence (IF) for FGFR4. RESULTS: I) FGFR4 is uniformly expressed in human gliomas, although at a varying degree, as confirmed by IHC, western blotting and RT-qPCR. II) FGFR4 expression was detected both in the nuclei and cytoplasm. III) Both a homogenous and a granular staining pattern was observed the cytoplasm, suggesting involvement of different cell types, whereas FISH demonstrated expression in the tumor and stromal cell compartments. IV) Tumors of grade II and III show a statistically significant higher expression than tumors of grade IV as shown by RT-qPCR. V) There is no difference in expression by IHC between tumors of grade II, III and IV. Citation Format: Christiane H. Gjerde, Ercan Mutlu, Lina Leiss, Bjarne Winther Kristensen, Mohummad Aminur Rahman, Per Øyvind Enger. FGFR4 is expressed in the tumor and stromal compartments of human gliomas of all grades and histologies. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1560. doi:10.1158/1538-7445.AM2015-1560