“…More complicated models with these assumptions and related bifurcation problems have also been studied by Cui, Escher and Zhou in the references [29][30][31]. In this paper we shall study the above tumor model without assuming that the unknown functions σ(x, y, t), p(x, y, t) and ρ(x, t) are periodic in the variable x, but instead we shall assume that these functions satisfy the following conditions as |x| → ∞: lim |x|→∞ σ(x, y, t), lim |x|→∞ p(x, y, t) and lim |x|→∞ ρ(x, t) exist, i.e., we shall consider the initial value problem of the model described by(1.1)-(1.6).…”