| 内容提要: |
Tumor metastasis refers to a process that tumor cells extend and spread to the surrounding tissues directly from the primary sites or settle down in distal tissues and progress to form new tumors through blood channel or lymphatic channel. In most cases, tumor cells of all sources have their fixed target organs in vivo, demonstrated by the in vitro experiment that this bunch of metastatic tumor cell was vulnerable to form tumor sites in specific locations in a sophisticatedly controlled condition. There are four stages of tumor metastasis process: (1) Cell detaching or intravasation: When tumor in situgrows to a certain size, tumor cells can secrete some active molecules which can regulate the characteristics of cells in situ on gene level and thus lead to reduction of pH value, increase of tumor cell surface charge and modification of glycoprotein structure on the cell surface. These changes enable tumor cells to release a subset from tumor tissues to the surrounding blood vessels or lymph vessels. (2) Cell transportation or migration: Detached tumor cells are transported or migrated to other normal organs with movement of blood or lymph: (3) Cell attaching or extravasation. Tumor cell mass in blood or lymph is blocked in the tiny blood vessel and thus stays there. Then tumor cells release bio‑enzymes that can destroy epithelialcells of normal tissues or peripheral connective tissues. After these bio‑enzymes destroy the surrounding tissues gradually, tumor cells can enter into the impaired tissues and combine with tumor matrix such as fibrous protein. (4) Angiogenesis or neovasculization: In oxygen deficit situation, matrix of the attached tumor cells can produce angiogenesis promoting factors with the effects of self‑regulatory mechanism, such as epithelial growth factor (EGF) and vascular endothelial growth factor (VEGF), which can promote formation of new vessels (generally speaking, it initiates obviously when the tumor diameter is up to 2mm). Tumor cells are then led to rapid growth via the nutrition transported by blood in the new vessels. |