Cancer is a group of more than 100 different diseases. It occurs when cells become abnormal and keep dividing and forming more cells without control or order. All organs of the body are made up of cells. Normally, cells divide to produce more cells only when the body needs them. If cells divide when new ones are not needed, they form a mass of excess tissue, called a tumor. Not all tumors are cancer – they can be benign (not cancer) or malignant (cancer). A few types of cancer, such as blood cancers, do not form tumors at all. The cells in malignant tumors can invade and damage nearby tissue and organs. Cancer cells can also break away form a malignant tumor and travel through the bloodstream or the lymphatic system to form new tumors in other parts of the body. The spread of cancer is called metastasis.
