Cancer starts in the body's cells. All of our organs and tissues are made up of cells. Each cell contains genes that determine how the cell grows, functions, and eventually dies.
There are a number of stages that a cell has to go through in order to replicate itself and they have to be accurate so that an exact copy of its chromosomes is distributed to the daughter cell. This means that each new cell contains an exact copy of the 46 chromosomes of the original chromosome and it's the reason why cells in a person's body are genetically identical.
Cancer starts with one normal cell changing into a cancerous cell; this may be due to a mutation in the cell's DNA that affects its growth. Once a cell in the body has changed in this way, it tends to multiply at a much more rapid rate than normal, and the bad cancerous cells proliferate and pile up. They undergo uncontrolled abnormal mitosis. These renegade cells escape the normal controls of mitotic cell division.
This mass of cancer cells is called a tumor and as it grows it releases proteins into the body to attract blood vessel growth to supply it with a steady stream of of food (glucose) and oxygen.
Cancer cells that have broken away from the tumor travel through the bloodstream and are taken to different parts of the body. From there they can start new tumors. This is a process known as metastasis. When someone is described as having a form of cancer, the term refers to the part of the body where the disease started.
