PLANTS THAT FIGHT CANCER
Everybody thinks it cannot happen to them. And yet, six million people die of cancer every year. Approximately every fourth citizen of a developed country will be stricken sometime during his life and approximately 400 new incidents emerge per 100,000 people annually. Once considered a mysterious disease, cancer has been eventually revealed to investigators (Trichopoulos and Hunter, 1996). Disease development begins from a genetic alteration (mutation) of a cell within a tissue. This mutation allows the cell to proliferate at a very high rate and to finally form a group of fast reproducing cells with an otherwise normal appearance (hyperplasia). Rarely, some hyperplastic cells will mutate again and produce abnormally looking descendants (dysplasia). Further mutations of dysplastic cells will eventually lead to the formation of a tumor, which can either remain localized at its place of origin, or invade neighboring tissues (malignant tumor) and establish new tumors (metastases). Cancer cells have some unique properties that help them compete successfully against normal cells: 1 Under appropriate conditions cancer cells are capable of dividing almost infinitely. Normal cells have a limited life span. As an example, human epithelial cells cultured in vitro are commonly capable of sustaining division for no more than 50 times (the so-called Hayflick number) (Hayflick and Hayflick, 1961). 2 Normal cells adhere both to one another and to the extracellular matrix, the insoluble protein mesh that fills the space between cells. Cancer cells fail to adhere and, in addition, they possess the ability to migrate from the site where they began, invading nearby tissues and forming masses at distant sites in the body, via the bloodstream. This process is known as metastasis and examples include melanoma cells migrating to the lung, colorectal cancer cells to the liver and prostrate cancer cells to bone. Although metastatic cells are indeed a small percentage of the total of cancer cells (e.g. 10 4 or 0.0001%), tumors composed of such malignant cells become more and more aggressive over time.
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