Modeling and analysis of nonlinear tumor-immune interaction under chemotherapy and radiotherapy

This paper examines the effects of treatment on tumor-immune dynamics based on a conceptual two-dimensional model. In absence of treatment, this model exhibits regimes of "active" and "dormant" tumor. Increasing intensity of chemotherapy entails a significant complication of tumor-immune interaction with parameter zones of monostability, bistability, and tristability where "active," "dormant," and "zero" tumor states can coexist. A detailed description of bifurcations, attractors, and their basins is given. Based on this mathematical analysis, we discuss efficiency of various programs of treatment combining chemotherapy and radiotherapy.