A simplified schematic of the tumour microenvironment and the roles of chemotaxis in the processes of: immune evasion (a), angiogenesis (b) and invasion and intravasation (c) in cancer. Grey arrows indicate the gradient direction of chemotactic factors: from the cell that secretes to the cell that responds to the factor. Black arrows indicate the direction of cell migration. The dashed grey line indicates matrix fibres along which cells migrate. CSF1, colony-stimulating factor 1; CSF1R, CSF1 receptor; EGF, epidermal growth factor; EGFR, EGF receptor; PDGF, platelet-derived growth factor; TGFβ, transforming growth factor-β; VEGF, vascular endothelial growth factor; VEGFR, VEGF receptor.