Acute lymphoblastic leukemia (ALL) is a type of cancer that causes the body to make too many white blood cells (lymphocytes). But these lymphocytes, called leukemia cells, cannot fight infection very well.

When leukemia cells build up in the blood and bone marrow, there is less room for healthy blood cells. This can cause infections, anemia, and easy bleeding.

ALL usually gets worse quickly. It is sometimes referred to as acute lymphocytic leukemia.

ALL is the most common type of childhood leukemia. It usually occurs in children ages 2 through 5 years. It may also occur in adults. ALL is the most successfully treated type of childhood leukemia.

Symptoms of ALL in children and adults include fever, weakness or feeling tired, bruising or bleeding easily, pinpoint spots under the skin from bleeding, bone pain, and loss of appetite.

ALL has several subtypes. A doctor can tell one from another by looking at ALL cancer cells. Each subtype has different proteins on the surface of a cell or different chromosome changes in a cell.

Knowing the type or subtype helps doctors plan the most effective treatment.