Cancer occurs when cells divide uncontrollably. These abnormal cells can invade nearby tissues or travel to distant sites by entering the bloodstream or lymphatic system.

For the human body to function normally, each organ must have a certain number of cells. The cells in most organs however have a short lifespan, and to continue functioning the body needs to replace these lost cells by the process of cell division.

Cell division is controlled by genes that are located in the cell nucleus. They function like an instruction manual telling the cell what proteins to make, how it will divide and how long it will live for. This genetic code can get damaged by a number of factors resulting in errors occurring within the instruction manual. These errors can dramatically alter how the cell functions. Instead of resting the cell may continue dividing, instead of dying the cell may stay alive.

A number of mechanisms are in place to prevent genetic errors from occurring and to eliminate genetically abnormal cells from the body. Yet in some people these defences are not enough and an abnormal population of cells that has escaped the bodies control develops. These cancer cells crowd out and destroy normal tissues.

Cancer cells require nutrients to survive and grow. Many types of cancer can stimulate blood vessel growth to provide them with the food they need. In fact the word cancer is derived from the latin word Cancri which means crab. It was thought by the ancients that the large blood vessels surrounding a tumour mass looked like a crabs claws and feet.