What is Leukemia?

Leukemia is cancer of the blood or bone marrow, characterized by an unusual increase in the number of the body's white blood cells. There is more than one kind of leukemia. It can be classified as either acute or chronic, and then further classified as lymphoid or myeloid.

Acute leukemia consists of a proliferation of immature blood cells that leads to the bone marrow being unable to produce healthy new blood cells. Acute leukemia can occur in both children and adults, and growth and accumulation of malignant cells occurs rapidly, making immediate treatment vital. Those cells can overflow into the bloodstream and then spread to other parts of the body. Untreated, a person with acute leukemia will die within months, or even weeks.

Chronic leukemia consists of an excessive build-up of somewhat mature, but still abnormal, blood cells. The cells are produced at a much higher rate than normal blood cells, and usually take months or years to progress. The result is an extreme amount of abnormal blood cells in the blood. Chronic leukemia occurs most often in older people, but is not impossible to find in any other age group. Chronic leukemia may be monitored for some time before beginning treatment, in order to ensure maximum effectiveness of treatment.

Leukemia is classified as lymphoid, or lymphocytic, leukemia when it affects the lymphoid cells, and myelogenous, or myeloid, leukemia when it affects the myeloid cells.

Using these two classification systems, there or four types of leukemia. Acute lymphocytic leukemia (also known as acute lymphoblastic leukemia, or ALL) is the most common form of leukemia in children, and also affects adults, especially those that are over the age of 65. Acute myelogenous leukemia (also known as acute myeloid leukemia, or AML) occurs more often in adults than children, and was formerly called acute nonlymphocytic leukemia. Chronic lymphocytic leukemia (also known as CLL) mostly affects adults over the age of 55. It can occur in younger adults, but is almost never found in children. Chronic myelogenous leukemia (also known as CML) occurs mainly in adults, and can also affect a very small number of children.

There is no definite known cause for any type of leukemia. Most likely, the different forms each have different causes. While little is known for sure about the origins of the disease, there are suspicions of four possible causes: ionizing radiation (natural or artificial), genetic predisposition, certain chemicals, and some viruses. Leukemia results from somatic mutations in a person's DNA that activate oncogenes and/or deactivate tumor suppressant genes. These mutations may occur randomly or result from exposure to radiation or carcinogenic substances, and are likely to be linked to heredity.

Until the cause or causes of leukemia are found, there is no way to prevent the disease. Treatment therapies and procedures vary with each form of the cancer.