Cancer is most easily understood as the development and sub­sequent spread throughout the body of cells from a malignant tu­mor. The unique feature of cancer cells is their readiness to multi­ply outside their organ of origin. The cells can be carried by the blood stream or the lymph system to other parts of the body where they grow. This growth can eventually destroy the healthy tissue that surrounds it. In the early stages cancerous tumors may be in­distinguishable from benign or harmless growths such as warts, moles or cysts.