Abstract Background: Bevacizumab, a monoclonal antibody targeting vascular endothelial growth factor A (VEGF-A), has proven activity in treatment of recurrent high-grade glioma. High response rates have been demonstrated, but particularly in WHO grade 3 malignant gliomas, efforts to identify predictors of clinical response have been limited. Predictive biomarkers and prognostic models are required in order to individualize treatment for this patient population. The primary end-point of this study was identification of prognostic and potentially predictive clinical and paraclinical factors of response. The secondary end-point was to identify prognostic factors associated with progression-free survival (PFS) and overall survival (OS). Materials and methods: A total of 64 recurrent grade 3 glioma patients treated with bevacizumab and irinotecan were retrospectively evaluated. Eligible patients from our center had a WHO performance status of 0-2 and were administered bevacizumab and irinotecan between December 2005 and November 2014 according to a previously published clinical protocol. The possibly relevant prognostic baseline factors screened for included: Age, gender, WHO grade 3 diagnosis, tumor size and location, multifocal disease, extent of resection, number of prior chemotherapy regiments, response to prior chemotherapy, first-line treatment, number of previous recurrences, neurological deficit, corticosteroid use, performance status, necrosis, vascular proliferation, neutrophil-to-lymphocyte ratio, and expression of p53, EGFR, Mib-1, MGMT, IDH-1 and ATRX. Candidate factors were subjected to univariate analysis and factors with P-values below 0.10 were considered for multivariate analysis. Prognostic models were generated by logistic regression and Cox regression, modeling response and survival end-points. P-values below 0.05 were considered statistically significant. Results will be presented. Citation Format: Anders Toft, Thomas Urup, Kirsten Grunnet, Ib J. Christensen, Signe R. Michaelsen, Helle Broholm, Vibeke A. Larsen, Michael Kosteljanetz, Ulrik Lassen, Hans S. Poulsen. Prognostic and predictive biomarkers of clinical response to Bevacizumab in recurrent WHO grade 3 malignant glioma patients. [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 5310. doi:10.1158/1538-7445.AM2015-5310