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 begins and gets worse quickly; patients with ALL usually need immediate treatment. ALL is most common in young children and adults older than 50, but people of any age can develop ALL.

About lymphocytes

Lymphocytes are made 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 stay 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 microbes and cancer cells. About 85% of people with ALL have the B-cell subtype and about 15% have the T-cell type. The NK-cell subtype is quite rare.

About ALL

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 (parts of the blood needed for clotting). This means that people with ALL may be anemic (because they do not have enough red blood cells), more likely to get infections (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 lymphatic system and cause swelling of the lymph nodes. Some cells may invade other organs, including the brain, liver, spleen, or the testicles in men.

Unlike other types of cancer, 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.

This section is about ALL in adults. Read about childhood ALL [2].

Find out more about basic cancer terms used in this section [3].

Looking for More of an Overview?

If you would like additional introductory information, explore these related items on Cancer.Net:

• Cancer.Net Patient Education Video [4]: View a short video led by an ASCO expert in this type of cancer that provides basic information and areas of research.

• Cancer.Net En Español [5]: Read about ALL in Spanish. Infórmase sobre leucemia linfocí­tica aguda en español.

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