When cells are “normal,” they grow and die in a controlled way. “Abnormal” or cancerous cells keep dividing and forming more cells without control. Cancer cells can invade nearby tissues and spread through the bloodstream and lymphatic system to other parts of the body. A tumor is an abnormal mass of tissue. When a tumor is cancerous, it is called malignant. (A non-cancerous tumor is referred to as benign.)

There are several main types of cancer: