Introduction to Acute Myelogenous Leukemia

The bone marrow is the spongy inner part of bones in which all of the different types of blood cells are made. Early (primitive) blood cells are called stem cells. As these stem cells mature, they develop into either red blood cells (RBCs), white blood cells (WBCs, leukocytes) or platelets.

Red blood cells are responsible for carrying oxygen from the lungs to all the tissues in the body, platelets play a critical role in blood clotting, and WBCs are important in fighting infection. There are three main types of WBCs: granulocytes, monocytes, and lymphocytes. The absence of normally functioning WBCs in leukemia weakens the body's ability to fight infections and the lack of normally functioning platelets makes leukemia patients more susceptible to bruising and bleeding.

Leukemia is a cancer of the blood cells and bone marrow. It is characterized by uncontrolled growth of blood cells. There are four major types of leukemia: acute or chronic myelogenous (AML, CML) and acute or chronic lymphocytic (ALL, CLL). The terms myelogenous and lymphocytic denote the morphology of the specific type of cells involved.

Acute leukemia is a rapidly progressing disease that results in the accumulation of immature, cells in the marrow and blood. These immature cells are called "blasts". Unlike the small percentage of blasts found in normal marrow, leukemic blasts are incapable of maturing. Furthermore, for unclear reasons, they also inhibit normal blasts from maturing. As a result, the marrow often can no longer produce enough normal red and white blood cells and platelets. Such bone marrow failure is the most common cause of death in AML. Chronic leukemia progresses more slowly and permits greater numbers of more mature functional cells to be made.

Because it is a disease of the blood cells, acute myelogenous leukemia does not usually form a solid mass or tumor. Although leukemia starts in the bone marrow, it can spread to the blood, lymph nodes, spleen, liver, central nervous system (CNS) and other organs.

Leukemia affects persons of all ages and both sexes, although the disease affects men somewhat more often than women. Approximately 31,000 new cases of leukemia were diagnosed in the United States in 2002. About one-half of these cases were acute leukemias and the other half chronic leukemias.

Acute Myelogenous Leukemia (AML), also called acute myeloid leukemia, is the most common type of acute leukemia in adults with approximately 10,100 new cases every year. About half the patients with AML are age 65 or over. Acute myelogenous leukemia accounts for just under half of cases of childhood leukemia.

The incidence of leukemia is about 10 times higher in adults than in children. Leukemia accounts for about 30% of all cancers in children under the age of 15. Approximately, 2,800 new cases of childhood leukemia were diagnosed in the United States in 2002. The most common form of acute childhood leukemia is acute lymphocytic leukemia (ALL).

There are several subtypes of acute myelogenous leukemia:

• Core-binding factor AML
• Acute Promyelocytic Leukemia (APL)
• Secondary AML
• Standard AML

Core-binding factor AML and APL are distinguished by their morphological appearance under the microscope (histology) and their chromosome abnormalities (cytogenetics). Secondary AML refers to AML developing after chemotherapy for a prior malignancy, for example breast cancer or a lymphoma such as Hodgkin's disease. As will be described below, different types of AML differ in prognosis and treatment. The core-binding factor leukemias and APL have the most favorable prognosis.