Figure 1.

A schematic model of the cancer (carcinoma) process leading to metastasis. The initial transformation of normal epithelial cells results in carcinoma in situ. With reduced adhesiveness and enhanced migratory behaviour, tumour cells progress to an invasive stage. After degradation of the basement membrane, cells invade the surrounding stroma, migrate and ‘intravasate’ into lymph or blood circulation. Surviving cells arrest in the capillaries of a distant organ. There, cells may remain dormant without reproliferating for considerable time. Alternatively, the tumour cells may exit the circulation (‘extravasate’) and lead to formation of secondary tumours occurs after proliferation, induction of angiogenesis and microenvironment activation. Modified from Bacac & Stamenkovic [1]. (Online version in colour.)