  We formulate and analyze a mathematical model describing immune response to
avascular tumor under the influence of immunotherapy and chemotherapy and their
combinations as well as vaccine treatments. The effect of vaccine therapy is
considered as a parametric perturbation of the model. In the case of a weak
immune response, neither immunotherapy nor chemotherapy is found to cause tumor
regression to a small size, which would be below the clinically detectable
threshold. Numerical simulations show that the efficiency of vaccine therapy
depends on both the tumor size and the condition of immune system as well as on
the response of the organism to vaccination. In particular, we found that
vaccine therapy becomes more effective when used without time delay from a
prescribed date of vaccination after surgery and is ineffective without
preliminary treatment. For a strong immune response, our model predicts the
tumor remission under vaccine therapy. Our study of successive chemo/immuno,
immuno/chemo and concurrent chemoimmunotherapy shows that the chemo/immuno
sequence is more effective while concurrent chemoimmunotherapy is more sparing.
