Leukemia is cancer of your body's blood-forming tissues, including the bone marrow and lymph system. The word leukemia means "white blood" in Greek. The disease usually starts in the white blood cells.

Under normal circumstances, your white blood cells are potent infection fighters. These cells normally grow and divide in an orderly, controlled way, as your body needs them. But leukemia disrupts this process.

In people with leukemia, the bone marrow produces a large number of abnormal white blood cells. They look different from normal blood cells and don't function properly. Eventually, they block production of normal white blood cells, impairing the ability to fight off infection. Leukemia cells also crowd out other types of blood cells produced by the bone marrow, including red blood cells, which carry oxygen to tissues throughout the body, and platelets, which help form blood clots that control bleeding.

Leukemia isn't just a children's disease, as some people think. Leukemia has four main types and many subtypes - and only some of them are common among children. Overall, this form of cancer affects about 10 times as many adults as children. Leukemia is usually fatal without successful treatment.

Signs and symptoms 

Signs and symptoms for each type of leukemia differ, but common symptoms include:

• Fever or chills

• Persistent fatigue, weakness

• Frequent infections

• Loss of appetite or weight

• Swollen lymph nodes, enlarged liver or spleen

• Easy bleeding or bruising

• Shortness of breath when you're physically active, such as while climbing steps

• Tiny red marks in the skin (petechiae)

• Excessive sweating, especially at night

• Bone pain or tenderness

The severity of signs and symptoms depends on the number of abnormal blood cells and where they collect. Early symptoms of leukemia may be overlooked because they may resemble symptoms of the flu and other common illnesses.