ABSTRACT
Tumours can arise from the cells of nearly all types of body tissue and this diversity of origin is largely responsible for the wide variety of the structural appearance of tumours. In this chapter we describe the main features of tumour growth and ways in which to model the processes involved. During the course of discussion we shall draw attention to some of the recent ideas and developments. In the earliest stages of development, tumour growth seems to be regulated by direct diffusion of nutrients and wastes from and to surrounding tissue. When a tumour is very small, every cell receives nourishment by simple diffusion and the growth rate is exponential in time. However, this stage cannot be sustained because, as a nutrient is consumed, its concentration must decrease towards the centre of the tumour. Eventually the concentration of a vital nutrient near the centre will fall below a critical level insufficient to sustain cell life. A central necrotic core then develops. The rate of growth of the tumour then falls away and it becomes more difficult to obtain nourishment and to dispose of wastes solely by diffusion.
