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Cancer starts when cells in a part of the body start to grow out of control. Cells in nearly any part of the body can become cancer. To learn more about what cancer is and how it starts, see What Is Cancer?

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. There are many types of leukemia. Here we will talk about acute myeloid leukemia (AML).

Normal bone marrow and blood cells

To understand the different types of leukemia, it helps to know about the bone marrow and types of blood cells. Any blood-forming cell 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.

Bone marrow

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.

Inside the bone marrow, blood stem cells develop into new blood cells. During this process, the cells become either lymphocytes (a kind of white blood cell) or other blood-forming cells, which are types of myeloid cells. These other blood-forming cells can develop into red blood cells, white blood cells (other than lymphocytes), or platelets.

Types of 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.

White blood cells help the body fight infections. There are many types of white blood cells. Each has a special role to play in protecting the body against infection. The main types of white blood cells are granulocytes, monocytes, and lymphocytes.

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.

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 this leukemia can grow quickly if not treated, and could be fatal in a few months. Myeloid refers to the type of cell this leukemia starts from.

AML is a cancer that starts in the cells that are supposed to mature into different types of blood cells (other than lymphocytes). AML starts in the bone marrow, 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.

AML isn’t the only kind of leukemia. There are other types as well. Knowing the exact type can help doctors better predict each patient's outlook (prognosis) and select the best treatment.

This section contains information on AML in adults only. To learn more about AML in children, see Childhood Leukemia. For information on other types of leukemia, see the leukemia section of our website.

Last Medical Review: 04/21/2015
Last Revised: 02/22/2016