What is acute lymphocytic leukemia?
Acute lymphocytic leukemia (ALL) is also called acute lymphoblastic leukemia. Leukemia is a type of cancer that starts in cells that form new blood cells. These cells are found in the soft, inner part of the bones called the bone marrow.
After it starts, leukemia often moves quickly into the blood where it can spread to other parts of the body such as the lymph nodes, spleen, liver, central nervous system (brain and spinal cord), and other organs. In contrast, other types of cancer can start in these organs and then spread to the bone marrow (or elsewhere). Those cancers are not leukemia. Both children and adults can get leukemia.
The term acute means that the leukemia grows quickly, and if not treated, could be fatal in a few months. Lymphocytic means it develops from early forms of lymphocytes, a type of white blood cell. This is different from acute myeloid leukemia (AML), which starts in other blood cell types found in the bone marrow. To learn about AML, please see our document, Leukemia--Acute Myeloid.
Other types of cancer that start in lymphocytes are known as lymphomas (non-Hodgkin lymphoma and Hodgkin disease). The main difference between these types of cancers is that the cancer cells in ALL are mainly in the bone marrow and blood (although they may spread to other places), while lymphomas are mainly in lymph nodes or other organs. For more information on lymphomas, see our documents, Non-Hodgkin Lymphoma and Hodgkin Disease.
Normal bone marrow, blood, and lymphoid tissue
In order to understand the different types of leukemia, it helps to know something about the blood and lymph systems.
Bone marrow is the soft, spongy, inner part of bones such as the skull, shoulder blades, ribs, pelvis, and bones in the spine. All of the different types of blood cells are made in the bone marrow. Bone marrow is made up of a small number of blood stem cells, blood-forming cells, fat cells, and tissues that help the blood cells grow.
Blood stem cells go through a series of changes to make new blood cells. They can develop into 1 of the 3 main types of blood cell:
- Red blood cells
- White blood cells
Red blood cells
Red blood cells carry oxygen from the lungs to all other tissues of the body. They also carry away carbon dioxide, a waste product of cell activity.
White blood cells
White blood cells help the body fight infections. There are quite a few types of white blood cells. Each has a special role to play in protecting the body against infection. The 3 main types of white blood cells are granulocytes, monocytes, and lymphocytes.
Lymphocytes are the main cells that make up lymphoid tissue (or lymphatic tissue), a major part of the immune system. The 2 main types of lymphocytes are called B-cells and T cells. Normal T cells and B cells do different jobs within the immune system. ALL starts in early forms of lymphocytes. It can start in either early B cells or T cells.
Platelets help stop bleeding by plugging up holes in blood vessels caused by cuts or bruises.
Any of the blood-forming cells can turn into a leukemia cell. Once that happens, the cell can grow and divide to form many new cancer cells. These cells can take over the bone marrow, spill out into the bloodstream, and spread to other organs.
Types of leukemia
Not all leukemias are the same. Leukemia is a complex disease with many different types and sub-types. Leukemias are divided into 4 main types. Knowing the exact type of leukemia can help doctors better predict each patient's outlook (prognosis) and select the best treatment.
The major types of leukemia are based on these factors:
- Acute or chronic
- Lymphocytic or myeloid
Acute leukemia vs. chronic leukemia
The first factor to take into account is whether most of the abnormal cells look like normal mature white blood cells or whether they look more like stem cells (they have not matured).
Acute leukemia: In acute leukemia, the bone marrow cells don't mature the way they should. These immature cells build up and crowd out normal cells. Without treatment, most patients with acute leukemia would live only a few months. Some types of acute leukemia respond well to treatment and many patients are cured. People with some other types do not do as well.
Chronic leukemia: In chronic leukemia the cells may look fairly normal, but they are not. They don't fight infection the way they should. They also live too long, so that they build up and crowd out normal bone marrow cells. Chronic leukemias tend to grow slowly over a longer time, and most patients can live for many years. But chronic leukemias are often harder to cure than acute leukemias.
Myeloid leukemia vs. lymphocytic leukemia
The second factor to take into account is the type of bone marrow cells that are involved.
Myeloid leukemia: Myeloid leukemia mainly develops from blood cells that are not lymphocytes. It starts in cells that form the other blood cells, such as granulocytes, monocytes, platelets, or red blood cells.
Lymphocytic leukemia: Lymphocytic leukemias develop from early forms of lymphocytes (a type of white blood cell).
Most leukemias can be sorted into 1 of the 4 main types shown in the table below.
Acute lymphocytic leukemia (ALL)
Acute myeloid leukemia (AML)
Chronic lymphocytic leukemia (CLL)
Chronic myeloid leukemia (CML)
Although ALL is the most common of the 4 major types of leukemia among children, it is the least common type among adults.
The rest of this document contains information on ALL of adults only. Chronic leukemias of adults and acute myelocytic leukemia (AML) of adults are discussed in other American Cancer Society documents. For information about ALL in children, please see the separate document, Childhood Leukemia.
Last Medical Review: 06/25/2012
Last Revised: 01/24/2013
- What Is Leukemia - Acute Lymphocytic (ALL) in Adults?
- Causes, Risk Factors, and Prevention
- Early Detection, Diagnosis, and Staging
- Treating Leukemia - Acute Lymphocytic (ALL) in Adults
- Talking With Your Doctor
- After Treatment
- What`s New in Leukemia - Acute Lymphocytic (ALL) in Adults Research?
- Other Resources and References