This chapter describes a model for the evolution of a spherically symmetric, non-necrotic tumour growing under the influence of both nutrients and growth inhibitory factors. Computational simulations are used to provide insight into the dynamics of the time-dependent problem studying the evolution of the growing tumour, while techniques from mathematical analysis (asymptotic analysis, two-timing method) are used to study the existence and stability of steady-state tumour configurations in which there is a balance between cell proliferation and cell death or apoptosis.