Classical and alternative activation of macrophages: different pathways of macrophage-mediated tumor promotion

Macrophages often function as control switches of the immune system, securing the balance between pro- and anti-inflammatory reactions. For this purpose and depending on the activating stimuli, macrophages can develop into different subsets: classically (M1) or alternatively (M2) activated macrophages, the characterization of which is a current topic of investigation. Accumulating evidence suggests that both populations, using their own specific mechanisms, may influence the behaviour of cancer cells, shape the tumor microenvironment and subverte anti-tumor immunity, thereby contributing to tumor growth and progression.