Figure 2.

Mechanism of cancer metastasis. A. Cancer cells produce proteases to destroy the surrounding matrix, and produce proteins to create new vessels. In cancer tissues, there are areas where the oxygen supply is poor, which induces hypoxia. Hypoxic cancer cells lose their adhesion characteristics and have enhanced capacity for migration. B. (1) Polyamines synthesized by cancer cells are transferred to cancer cells under hypoxic conditions that have increased capacity for polyamine uptake and decreased intracellular polyamine synthesis. The increase in polyamine concentration due to increased polyamine uptake decreases adhesion of cancer cells by decreasing adhesion molecule expression. (2) Polyamines are transferred to the blood cells. Increased polyamine uptake by immune cells results in decreased production of tumoricidal cytokines and the amount of adhesion molecules, and these eventually attenuate the cytotoxic activities of immune cells.