Leukemias, Acute Health Article

Definition

Acute leukemia is a type of cancer in which excessive quantities of abnormal white blood cells are produced.

Description

Medical science further classifies acute leukemia by the type of white blood cell that undergoes mutation. The most common of these are:

• Acute lymphoblastic leukemia (ALL), in which excessive quantities of lymphoblasts, or immature lymphocyte white blood cells, are produced.
• Acute myeloblastic leukemia (AML), also known as acute nonlymphocytic leukemia (ANLL), in which excessive quantities of other types of immature white blood cells are produced.

Acute leukemias progress rapidly, while the chronic leukemias progress more slowly. The vast majority of the childhood leukemias are of the acute form.

The cells that make up blood are produced in the bone marrow and the lymphatic system. Bone marrow is the spongy tissue found in the large bones of the body. The lymphatic system includes the spleen (an organ in the upper abdomen), the thymus (a small gland beneath the breastbone), and the tonsils (a mass of lymphatic tissue located in the throat). In addition, the lymphatic vessels (tiny tubes that branch like blood vessels into all parts of the body) and lymph nodes (pea-shaped organs that are found along the network of lymphatic vessels) are also part of the lymphatic system. Lymph is a milky fluid that contains cells. Clusters of lymph nodes are found in the neck, underarm, pelvis, abdomen, and chest.

The cells found in the blood include red blood cells (RBCs) that carry oxygen and other materials to all tissues of the body; white blood cells (WBCs) that fight infection; and platelets, which play an important role in the clotting of the blood. White blood cells can be further subdivided into three main types: granulocytes, monocytes, and lymphocytes.

The granulocytes, as their name suggests, have particles (granules) inside them. These granules contain special proteins (enzymes) and several other substances that can break down chemicals and destroy microorganisms, such as bacteria. Monocytes are the second type of white blood cell. They are also important in defending the body against pathogens.

Lymphocytes are the third type of white blood cell. There are two primary types of lymphocytes—T lymphocytes and B lymphocytes—with different functions in the immune system. B cells protect the body by making antibodies. Antibodies are proteins that can attach to the surfaces of bacteria and viruses. This "attachment" sends signals to many other cell types to come and destroy the antibody-coated organism. T cells protect the body against viruses. When a virus enters a cell, it produces certain proteins that are projected onto the surface of the infected cell. T cells recognize these proteins and make certain chemicals that are capable of destroying the virus-infected cells. In addition, T cells can destroy some types of cancer cells.

Bone marrow makes stem cells, which are the precursors of the different blood cells. These stem cells mature through stages into either RBCs, WBCs, or platelets. In acute leukemias, the maturation process of the white blood cells is interrupted. The immature cells (or "blasts") proliferate rapidly and begin to accumulate in various organs and tissues, thereby affecting their normal function. This uncontrolled proliferation of the immature cells in the bone marrow affects the production of the normal red blood cells and platelets as well.

As noted, there are two types of acute leukemias—acute lymphocytic leukemia and acute myelogenous leukemia. Different types of white blood cells are involved in the two leukemias. In acute lymphocytic leukemia (ALL), it is the T or the B lymphocytes that are involved. The B cell leukemias are more common than T cell leukemias. Acute myelogenous leukemia, also known as acute nonlymphocytic leukemia (ANLL), is a cancer of the monocytes and/or granulocytes.

Leukemias account for 2% of all cancers. Because leukemia is the most common form of childhood cancer, it is often regarded as a disease of childhood. However, leukemias affect far more adults than children. Half of the cases occur in people who are 60 years of age or older. The incidence of acute and chronic leukemias is about the same. According to the estimates of the American Cancer Society (ACS), approximately 29,000 new cases of leukemia are diagnosed each year in the United States. Of these, 27,000 will be diagnosed in adults, 2,000 in children.