What is acute myeloid leukemia?

Acute myeloid leukemia (AML) goes by many names, including acute myelocytic leukemia, acute myelogenous leukemia, acute granulocytic leukemia, and acute non-lymphocytic leukemia. Acute means that the leukemia can grow quickly, and if not treated, could be fatal in a few months.

AML is a cancer that starts in the cells that are supposed to mature into different types of blood cells. AML starts in the bone marrow (the soft inner part of the bones, where new blood cells are made), but in most cases it quickly moves into the blood. It can sometimes spread to other parts of the body including the lymph nodes, liver, spleen, central nervous system (brain and spinal cord), and testicles (in men).

In contrast, other types of cancer can start in these organs and then spread to the bone marrow (or other places). Those cancers are not leukemia.

(A type of acute leukemia that starts in lymphocytes is called acute lymphocytic leukemia or ALL. To learn more about this type of leukemia, see our document called Leukemia: Acute Lymphocytic.)

Normal lymph tissue, bone marrow, and blood cells

In order to understand the different types of leukemia, it helps to know something about the lymph (pronounced "limf") and blood systems.

Lymph system

The immune system is made up mainly of lymph tissue (also known as lymphatic or lymphoid tissue). The main cell type that forms lymph tissue is the lymphocyte, a kind of white blood cell. (White blood cells help the body fight infections.) 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 in order to find and kill germs.

Bone marrow and blood cells

Bone marrow is the soft, spongy, inner part of bones. It is found in some bones such as the skull, shoulder blades, ribs, pelvis, and backbones. All of the blood cells are made in the bone marrow. Bone marrow is made up of blood stem cells, blood-forming cells, fat cells, and tissues that help blood cells grow.

Blood stem cells go through a series of changes to make new blood cells. (They are different from embryonic stem cells which are from a developing fetus and can grow to become other kinds of cells in the body.) During this process, the cells develop into either lymphocytes (a kind of white blood cell) or other blood-forming cells. The blood-forming cells can develop into 1 of the 3 main types of blood cell: red blood cells, white blood cells, or platelets.

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 cell waste product. A shortage of red blood cells causes a person to feel tired, weak, and short of breath.

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.

Platelets: Platelets are actually pieces that break off from certain bone marrow cells. Platelets help stop bleeding by plugging up holes in blood vessels caused by cuts or bruises. A shortage of platelets can cause a person to bleed or bruise easily.

Any of the blood-forming cells can turn into a leukemic cell. Once that happens, the cell can 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; they are divided into 4 main types. Knowing the exact type of leukemia can help doctors better predict each patient's outlook (prognosis) and choose the best treatment.

The major types of leukemia are based on whether the disease is:

• Acute or chronic
• Lymphocytic or myeloid

Acute leukemia versus chronic leukemia

The first factor used to classify a patient's leukemia is whether most of the changed (abnormal) cells look like normal mature white blood cells or whether they look more like stem cells (cells that 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 other types may not do as well.

Chronic leukemia: In chronic leukemia the cells look a lot like normal white blood cells, but they are not. They can't fight infection the way they should. They also live too long, so they build up and crowd out normal bone marrow cells. Chronic leukemias tend to progress over a longer period of time, and most patients can live for many years. But chronic leukemias are often harder to cure than acute leukemias.

Myeloid leukemia versus lymphocytic leukemia

The second factor to take into account is the type of bone marrow cells that are involved.

Myeloid leukemia: Myeloid leukemia mainly starts in white blood cells like granulocytes or monocytes. But it can also start in the cells that mature into platelets or red blood cells.

Lymphocytic leukemia: Lymphocytic leukemias develop from lymphocytes (a different type of white blood cell) in the bone marrow.

Most cases of leukemia can be sorted into 1 of the 4 main types shown in the table below.

The rest of this document contains information on AML of adults only. To learn more about AML in children, please see our document, Childhood Leukemia.

Chronic leukemias of adults and acute lymphocytic leukemia (ALL) of adults are discussed in other American Cancer Society documents.