Abstract Purpose: Vascular endothelial growth factor (VEGF) inhibition is a validated cancer treatment. However, even in responsive tumors, acquired resistance is common. Notch proteins also function as key angiogenic effectors, and cross-regulate VEGF expression, raising the question of whether combined treatment would enhance tumor suppression. We hypothesized that dual VEGF/Notch blockade would inhibit tumor growth in experimental SY5Y neuroblastoma. Methods: SY5Y neuroblastoma cells were lentivirally transfected to express Notch1-decoy (N1D) or GFP (control). Proliferation was assessed in vitro under both hypoxia and normoxia using BrdU assays. To examine the effect of N1D on tumor growth, 10[6] cells were xenografted intrarenally in nude mice and treated with placebo or bevacizumab (BV) twice a week. Tumor progression was monitored by bioluminescence. Metastatic burden in target organs was quantified by bioluminescence and histology. Vascular disruption due to N1D and BV treatment was evaluated by immunostaining. IACUC approval was obtained for all experiments. Results: Expression of soluble N1D was confirmed by immunoblotting conditioned media. SY5Y+N1D cells proliferated more rapidly in hypoxia than control SY5Y+GFP cells (p<0.01). In vivo, BV treatment alone significantly reduced tumor growth as compared to placebo (p=0.026). However, combined treatment (N1D + BV) did not further reduce SY5Y tumor growth as compared to BV treatment alone (p=0.684). Interestingly, dual-treated mice developed higher metastatic burdens in liver than mice treated with either agent alone or controls by bioluminescence (p=0.006). By histology, dual-treated mice displayed a higher incidence of liver metastasis (7/9 mice) vs. mice treated with BV only (3/10 mice). Immunostaining demonstrated disruption of tumor vessel architecture in BV- and N1D + BV-treated mice. Conclusion: Dual VEGF/Notch targeting of SY5Y tumors resulted in increased metastatic burden, without affecting primary tumor growth, as compared to either treatment alone. Recent data indicates that tumoral hypoperfusion can promote progression, potentially by selecting for biologically aggressive behaviors. Our results suggest that dual Notch/VEGF blockade causes an enhanced propensity to metastasize. These data warrant further preclinical investigation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2325. doi:1538-7445.AM2012-2325