Overview

Leukemia is a cancer of the blood. Leukemia begins when normal blood cells change and grow uncontrollably. Acute lymphocytic leukemia (ALL) is a cancer of the lymphocytes, a type of white blood cell involved in the body’s immune system. ALL is also called acute lymphoid leukemia or acute lymphoblastic leukemia. Acute means that the disease appears and advances quickly; patients with ALL usually require immediate treatment. ALL is most common in young children and adults older than 50, but it can occur at any age.

Lymphocytes are produced in the bone marrow, the spongy, red tissue in the inner part of the large bones. Lymphocytes are found in the blood, lymph nodes, and spleen. Healthy lymphocytes fight bacterial and viral infections. In people with ALL, new lymphocytes do not develop into mature cells, but remain as immature cells called lymphoblasts.

There are three different types of lymphocytes: T cells, B cells, and natural killer (NK) cells. Generally, T cells fight infections by activating other cells in the immune system and by destroying infected cells, B cells make antibodies, and NK cells fight microbial cells and cancer cells. Approximately 85% of ALL cases are the B-cell subtype, and about 15% are of T-cell type. The NK-cell subtype is quite rare.

In people with ALL, the abnormal cells crowd other types of cells in the bone marrow, preventing the production of red blood cells (which carry oxygen), other types of white blood cells, and platelets (blood components needed for clotting). This means that people with ALL may be anemic (because they do not have enough red blood cells), susceptible to infection (because they do not have enough of the type of white blood cells called neutrophils that fight bacteria), and bruise or bleed easily (because of a low level of platelets). Lymphoblasts may also collect in a person’s lymph tissues and cause swelling of the glands. Some cells may invade other organs, including the brain, liver, spleen, or the testicles in men.

The spread of ALL to other parts of the body does not mean the cancer is in an advanced stage, because acute leukemia is usually found throughout the body when it is diagnosed.