字幕列表 影片播放 列印英文字幕 Spread of tumors to distant locations is of great importance in cancer About ninety percent of the deaths due to cancer involve tumors that have spread around the body. The movement of tumor cells to other parts of the body is known as metastasis. Metastasis is a complex process During which cancer cells break off the original or primary tumor and move through the body to form tumors at new locations From the point of view of a cancer cell, this is a dangerous and often unsuccessful process A trip through the body is full of hazards that cause the death of most cells that begin the journey even tough cancer cells. To begin the process individual cells must break away from the tumor and invade nearby vessels The cells crawl along the surface of other cells and the fibrous stringy structures surrounding them and then force their way in. Shown here is the invasion of the blood supply. Once inside a blood vessel, the cancer cells may parish from a variety of causes Some cells die simply because they are unable to survive floating around in the bloodstream. Others may become damaged and die when they squeeze through tight spaces or bump into the walls of the blood vessels. Still other migrating cells may be recognized and destroyed by cells of the immune system. How and where the migrating cells stop is different for different cancer types Once the tumor cells are no longer moving they can begin the process of forming a new tumor by leaving the blood vessel and beginning to reproduce in the new location This does not always occur and cells that have made it this far may still die or fail to divide If the new environment is suitable the newly-arrived cell will begin to grow and a new tumor will develop.