Fig 8. Simulation of the PDE model (12a)–(12g) for several values of the division rate a.

Evolution of the tumor mass μ₁ (plain, left axis), and of the immune strength ${\overline{\mu }}_c$ (defined in (26), dashed, right axis); expected equilibrium value λ (dotted line in fig. (a) and (b)). When a is small enough an equilibrium is reached with ${\overline{\mu }}_c$ tending to the eigenvalue λ of the cell-division equation, and a residual tumor mass (fig. (a) and (b)). For larger a’s the tumor escapes the control of the immune system and its mass bows up (fig. (c) and (d)): mind the different time scales, since the blows up is faster as a increases.