3095 Background: Inhibition of tumor angiogenesis is one of the intensively investigated new approaches for cancer treatment. ANG1 is a protein that promotes interaction of endothelial cells with pericytes and supports vascular maturation. Previously we analyzed tumor angiogenesis by constructing a detailed computer model of vascular tumor growth, which included the behavior of VEGF, PDGF, ANG1, ANG2, etc. The model simulations were successful in retrieving in vivo experimental results. In the current work we used the model to analyze the effect of ANG1 production on disease progression. Methods: Experimental individual growth curves of human ovarian carcinoma xenografts in nude mice were used to estimate parameters of tumor and vasculature dynamics. These parameters served as input to the aforementioned model, for simulating the stimulation or inhibition of ANG1 production. Results: Different individual tumor growth curves were retrieved with high precision, by individually estimated sets of dozens of model parameters. Analysis of these parameter sets showed that they varied only in the vascular density at the implantation site and in the tumor secretion rates of angiogenic factors; this variability sufficed for yielding the different growth curves. The modulation of ANG1 production appeared to have a complex effect: In rapidly growing tumors a specific ANG1 production level induced maximal tumor growth, while both higher and lower levels caused relative tumor growth suppression. In slow growing tumors inhibition of ANG1 production accelerated tumor growth, while its stimulation had little effect. Conclusions: Our analysis suggests that the induction as well as the inhibition of ANG1 production by tumor cells can have different and even opposite effects on tumor growth, depending on the patho-physiological conditions. Using medically retrievable parameters of tumor and vasculature dynamics our model can suggest optimal therapeutic interventions by ANG1 modulation. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Optimata Ltd. Optimata Ltd.