Leukemia is the name of a group of cancers of the blood cells. Almost 27,000 adults and more than 2,000 children in the United States are diagnosed with leukemia each year. There are different types of leukemia and several treatment options for each type. This reference summary explains what leukemia is and reviews its causes, symptoms, diagnosis, and treatment options. Cancer The body is made up of very small cells. Normal cells in the body grow and die in a controlled way. Sometimes cells keep dividing and growing without normal controls, causing an abnormal growth called a tumor. If a tumor does not invade nearby tissues and body parts, it is called a benign tumor, or non-cancerous growth. Benign tumors are almost never life threatening. If the tumor invades and destroys nearby cells, it is called a malignant tumor, or cancer. Cancer can sometimes be life threatening. Cancerous cells sometimes spread to different parts of the body through blood vessels and lymph channels.