Stochastic dynamics of nonlinear tumor-immune system with chemotherapy

Motivated by important applications to the solution of the problem of studying the mechanisms of tumor treatment, we consider a model of the dynamic interaction of tumor and immune cells under chemotherapy and random disturbances. Through the bifurcation analysis of the deterministic model, changes in dynamic modes, equilibrium and oscillatory, are studied depending on the therapy intensity parameter. The deformations of these regimes caused by random perturbations, namely stochastic excitation, noise-induced transitions in bistability zones, and noise-induced tumor suppression, are investigated numerically and using the analytical technique of stochastic sensitivity and the confidence domains method.