Acute myeloid leukemia (AML) is a type of leukemia, or cancer of the body’s blood-forming cells. Also known as acute myelogenous leukemia, it affects the body’s blood making system which includes bone marrow and the lymphatic system.  Although the abnormal cells of AML initially develop in the bone marrow, they typically spread quickly into the blood and eventually they may spread further to other organs.

Bone marrow is the soft, inner component of bones. It is composed of blood-forming cells, fat cells, and supportive tissues. All forms of blood cells are produced in the bone marrow from a cell called the stem cell. Blood cells produced from stem cells in the bone marrow include:

• White blood cells (cells that are involved in the immune system and fight infection). The three main types of white blood cell include:
  
  
• Granulocytes (neutrophils, basophils, and eosinophils)
• Monocytes
• Lymphocytes
  
  
• Red blood cells (cells that carry oxygen to tissues all over the body).
  
  
• Platelets (cells that help develop blood clots and control bleeding).

In AML, the stem cells that normally develop into cells called myeloblasts fail to mature into healthy white blood cells. Because they are defective, the cells are unable to defend the body from disease. Although the condition occurs rarely in people with AML, stem cells can develop into a large number of abnormal red blood cells (erythroblasts) or platelet-producing cells (megakaryoblasts). These produce uncommon forms of AML.

As the leukemia progresses, the levels of abnormal cells gradually build up in the blood and bone marrow, crowding out normal white blood cells, red blood cells and platelets. As a result, production of normal white blood cells decrease, and the body’s ability to fight infection is impaired. In addition, the decrease in production of red blood cells and platelets results in anemia and bleeding disorders.

There are many different types and subtypes of leukemia. In general, the disease is first classified according to whether the majority of abnormal cells are mature or immature.  Leukemia developing from immature cells is classified as acute while leukemia developing from more mature cells is classified as chronic. The second classification is based on the exact type of cell from which the leukemia developed. Leukemia can develop in two forms of blood cells, lymphocytes and myeloid cells

AML is classified as a myeloid leukemia because it develops from myeloid cells. These are cells that eventually develop into red blood cells, white blood cells, and platelet-producing cells (megakaryocytes). It is classified as acute because it develops from immature cells known as blast cells. Acute forms of leukemia develop quickly and, without proper treatment, are fatal within a few weeks to a few months.

Another form of myeloid leukemia is chronic myeloid leukemia. Although this type of leukemia also develops from myeloid cells, it differs from AML because it develops from more mature cells (chronic).

According to the American Cancer Society (ACS), more than 44,000 new cases of leukemia will be diagnosed in the United States in 2007. Of these new cases, about 13,500 will be AML. It is the most common form of leukemia, and more than 90 percent of AML cases occur in adults, with the average age being over 65. In addition, the disease is more common in men than in women.