Mathematical modeling of tumor growth dynamics may have great impact on modern medicine. The dynamical model of tumor growth which describes the effect of drugs can be used e.g., for therapy optimization, therapy supervision, drug development. Based on a single drug tumor growth model, we create a model that can be used to describe the effect of two drugs. The extended model is created using formal reaction kinetics analogy, thus the meaning of the equations is interpretable for experts not familiar with differential equations. We carry out parametric identification using nonlinear mixed-effect model, for the identification we use measurements from mice experiments carried out using bevacizumab and fluorouracil treatment. The results of the identification show that the measurements can be reproduced using the model with small error, and the interpatient variability for most of the parameters is relatively low.