Leukemias, Chronic Health Article

Definition

Chronic leukemia is a type of cancer in which excessive quantities of abnormal white blood cells are produced, usually slowly, often over a period of years.

Description

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

• Chronic lymphocytic leukemia (CLL), in which mature-appearing white blood cells called lymphocytes are produced.
• Chronic myeloid (or myelogenous) leukemia (CML), also known as chronic granulocytic leukemia (CGL), is the result of uncontrolled proliferation of white blood cells called granulocytes.

Chronic leukemias are much less rapid-growing than acute leukemia, and affect adults far more often than children. In fact, nearly all the people who develop CLL are over 50 years of age. CML is also a disease primarily of middle-aged to elderly people, but 3% of all childhood leukemias are classified as CML, and the average age for developing CML is between ages 10 and 12.

The cells that make up blood are produced in the bone marrow and the lymph system. The bone marrow is the spongy tissue found in the large bones of the body. The lymph system includes the spleen (an organ in the upper abdomen), the thymus (a small organ beneath the breastbone), and the tonsils (an organ in the throat). The lymph vessels (tiny tubes that branch like blood vessels into all parts of the body) and lymph nodes (small peashaped organs that are found along the network of lymph vessels) are also part of the lymph system. The lymph itself 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 are the red blood cells (RBCs), which carry oxygen and other materials to all tissues of the body; white blood cells (WBCs), which fight infection; and the platelets, which play an important role in the clotting of the blood. The white blood cells can be further subdivided into three main types: granulocytes, monocytes, and lymphocytes.

The granulocytes have particles (granules) inside them that 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.

The lymphocytes form the third type of white blood cell. The two primary types of lymphocytes, T lymphocytes and B lymphocytes, have different functions within the immune system. The B cells protect the body by making antibodies, which are proteins that can attach to the surfaces of bacteria and viruses. This attachment sends signals to many other cell types to destroy the anti-body-coated organism. The 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. The T cells recognize these proteins and make certain chemicals that are capable of destroying the virus-infected cells. In addition, the T cells can destroy some types of cancer cells.

The bone marrow makes stem cells, which are the precursors of the different blood cells. Stem cells mature into RBCs, WBCs, or platelets. In chronic leukemias, blood cells suddenly begin to 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.

Different types of white blood cells are involved in chronic lymphocytic leukemia and chronic myeloid leukemia. Although some blasts, or immature cells (the hallmark of acute leukemia), are also present in chronic leukemia, it is the T or B lymphocytes that gradually mutate and become cancerous. The scenario is similar for chronic myelogenous leukemia, also known as chronic granulocytic leukemia (CGL), which occurs when unusually large numbers of granulocytes begin to appear in the bloodstream.

Leukemias account for 2% of all cancers. 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, 2000 in children. Leukemia is the most common form of childhood cancer, and it is often regarded as a disease of childhood However, leukemias, especially chronic leukemia, affect far more adults than children. Half of all leukemia cases occur in people who are 60 years of age or older, and the over-whelming majority of chronic leukemias occur in adults. The incidence of both acute and chronic leukemias is about the same.