FIGURE 1. Microecology of the tumour–host invasion field.

Invasive carcinoma is viewed as a pathology of multiple cell societies inhabiting the epithelial/mesenchymal stromal unit. Transition to invasive carcinoma is preceded by the activation of host fibroblasts, immune cells and endothelial cells. Invasion occurs in a localized zone of cross-talk and cooperation between the stromal cells and the premalignant epithelium (depicted as zones demarked by dashed lines). Cytokine and enzyme exchange between the participating cells stimulates migration of both cell types towards each other and modifies the adjacent extracellular matrix/basement membrane. The result is a breakdown of normal tissue boundaries.