Modelling the macrophage invasion of tumours: Effects on growth and composition

E-mail: owen{at}maths.warwick.ac.uk E-mail: jas{at}maths.warwick.ac.uk Even in the early stages of their development, tumours are notsimply a homogeneous grouping of mutant cells; rather, theydevelop in tandem with normal tissue cells, and also recruitother cell types including lymphatic cells and the endothelialcells required for the development of a blood supply. It hasbeen repeatedly seen that macrophages form a significant proportionof the tumour mass, and that they can have a variety of effectsupon the tumour, leading to a delicate balance between growthpromotion and inhibition. This paper develops a model for theearly, avascular growth of a tumour, concentrating on the inhibitoryeffect of macrophages due to their cytolytic activity. It isshown that such an immune response is not sufficient to preventgrowth, due to it being a second-order process with respectto the density of the tumour cells present However, the presenceof macrophages does have important effects on the tumour composition,and the authors perform a detailed bifurcation analysis of theirmodel to clarify this. An extended model is also consideredwhich incorporates addition of exogenous chemical regulators.In this case, the model admits the possibility of tumour regression,and the therapeutic implications of this are discussed.