What is acute myeloid leukemia?
Cancer arises when cells in a part of the body begin to grow out of control and can spread to other areas of the body. There are many types of cancer. Cells in almost any part of the body can become cancer. To learn more about how cancers begin and spread, read What is cancer?
Leukemias are cancers that originate in cells that would normally mature into different types of blood cells. This article provides information about acute myeloid leukemia (AML).
Acute myeloid leukemia (AML) is also known by many other names, including acute myelocytic leukemia, acute myelogenous leukemia, acute granulocytic leukemia, and acute non-lymphocytic leukemia.
The term "acute" means that this leukemia can progress rapidly and, if left untreated, is likely to be fatal within a few months. The term "myeloid" refers to the type of cell from which this leukemia originates.
Most cases of AML originate from cells that would become white blood cells (but not lymphocytes), but in some cases AML develops in other types of blood-forming cells. The different types of AML are presented in the section "How is acute myeloid leukemia classified?".
Acute myeloid leukemia begins in the bone marrow (the soft inner part of certain bones, where new blood cells are made), but in most cases it quickly passes into the blood. Sometimes it spreads to other parts of the body, including the lymph nodes, the liver, the spleen, the central nervous system (the brain and spinal cord) and the testicles.
Sometimes it spreads to other parts of the body, including the lymph nodes, the liver, the spleen, the central nervous system (the brain and spinal cord) and the testicles. Other cancers can start in these organs and then spread to the bone marrow, but these cancers that start elsewhere and then spread to the bone marrow are not leukemias.
Bone marrow, blood and normal lymphatic tissue
To understand the different types of leukemia, it helps to know about the blood and lymphatic systems.
Bone marrow
The bone marrow is the soft inner portion of some bones such as the skull, shoulder blades, ribs, bones of the pelvis (hip) and spine. The bone marrow consists of a small number of blood stem cells, more mature blood-producing cells, adipose cells and supporting tissues that help cell growth.
Inside the bone marrow, the blood stem cells become new blood cells. During this process, the cells become lymphocytes (a type of white blood cell) or other blood-producing cells, which are types of myeloid cells. These other blood-producing cells can develop into red blood cells, white blood cells (which are not lymphocytes) or platelets.
Types of blood cells
Red blood cells carry oxygen from the lungs to all other tissues in the body, and carry carbon dioxide to the lungs for removal. An insufficient amount of red blood cells in the body (anemia) can cause fatigue, weakness and difficulty breathing because the body's tissues do not receive enough oxygen.Platelets are actually cell fragments produced by a type of bone marrow cell called a megakaryocyte. Platelets are important in stopping bleeding because they help plug the holes in the blood vessels caused by cuts or bruises. Having too few platelets (thrombocytopenia) can make you bruise or bleed easily.
White blood cells help the body fight infections. Having too few white blood cells weakens your immune system and you may be more likely to get an infection.
Types of white blood cells
Lymphocytes are mature cells that fight infections that develop from lymphoblasts, a type of blood stem cell in the bone marrow. Lymphocytes are the main cells that make up the lymphatic tissue, which is an important part of the immune system. The lymphatic tissue is found in the lymph nodes, the thymus (a small organ behind the sternum), the spleen, the tonsils and the adenoid glands, and is disseminated through the digestive and respiratory systems and the bone marrow. There are two main types of lymphocytes:
B lymphocytes (B cells) protect the body against invading germs by developing (maturing) to form plasma cells, which produce proteins called antibodies. Antibodies adhere to germs (bacteria, viruses, and fungi), which helps other types of white blood cells to recognize and destroy them.
T lymphocytes (T cells) can recognize cells infected with viruses and destroy them directly. They also help regulate the immune response.
Granulocytes are mature cells that fight infections that develop from myeloblasts, a type of blood-producing cell in the bone marrow. Granulocytes have granules that appear as spots when viewed under a microscope. These granules contain enzymes and other substances that can destroy germs like bacteria. The three types of granulocytes, neutrophils, basophils and eosinophils, are distinguished by the size and color of the granules.
Monocytes develop from blood-producing monoblasts in the bone marrow and are related to granulocytes. After circulating in the bloodstream for about a day, monocytes enter the body tissues to become macrophages, which can destroy some germs by surrounding and digesting them. Macrophages also help lymphocytes recognize germs and produce antibodies to fight them.
Any of the lymphoid or myeloid blood forming cells of the bone marrow can become a leukemic cell. Once this change occurs, the leukemia cells no longer mature in a normal way. Leukemic cells often reproduce rapidly, but in most cases the problem is that they do not die when they should, but they survive and accumulate in the bone marrow. With the passage of time, these cells enter the bloodstream and spread to other organs, where they can prevent other cells in the body from performing their functions.
Types of leukemia
Not all leukemias are the same. There are four main types of leukemia. When the doctors know the specific type that the patient suffers, they can make a better prognosis (have a better perspective) and select the best treatment.
Acute leukemia versus chronic leukemia
The first factor in classifying a patient's leukemia is whether most of the abnormal cells look like normal (mature) white blood cells or rather look like (immature) stem cells.In acute leukemia, leukemic cells are immature blood cells (blasts). These leukemias are fast-growing because normal blast cells divide rapidly. However, leukemia cells do not divide more rapidly than normal blast cells, they simply do not stop dividing when normal blast cells do. 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 can be cured. Other types of acute leukemia have a less favorable outlook.
On the other hand, in chronic leukemia, leukemia cells are more mature but are not completely normal. In general, they do not fight infections as well as normal white blood cells, and they survive longer, accumulate and displace normal cells. Chronic leukemias tend to progress for a longer period of time, and most patients can live with them for many years. However, chronic leukemias are generally more difficult to cure than acute leukemias.
Myeloid leukemia against lymphocytic leukemia
The other important factor in classifying leukemia is the type of cells in the bone marrow that are affected.
Myeloid leukemias originate in the immature forms of myeloid cells (white blood cells [other than lymphocytes], red blood cells, or platelet-producing cells [megakaryocytes]). These are also known as myelocytic, myelogenous or non-lymphocytic leukemia.
Lymphocytic leukemias originate in the immature stages of lymphocytes. They are also known as lymphoid or lymphoblastic leukemias. Lymphomas are also cancers that originate in lymphocytes. However, unlike the lymphocytic leukemias that develop in the bone marrow, lymphomas develop from cells in the lymph nodes or other organs.
Depending on whether the leukemias are acute or chronic, and whether they are myeloid or lymphocytic, they can be divided into four main groups:
Acute myeloid (or myelogenous) leukemia (acute myeloid leukemia, AML)
Chronic myeloid (or myelogenous) leukemia (chronic myeloid leukemia, CML)
Acute lymphocytic (or lymphoblastic) leukemia (acute lymphocytic leukemia, ALL)
Chronic lymphocytic leukemia (CLL)
The rest of this document focuses on acute myeloid leukemias in adults only. Chronic leukemias in adults and acute lymphocytic leukemia (ALL) in adults are discussed in other documents of the American Cancer Society. For information on AML in children, see the document Leukemia in children.
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