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Overview of Leukemia

by Michael E. Rytting, MD

Leukemias are cancers of white blood cells or of cells that develop into white blood cells.

White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry, and pieces of chromosomes get rearranged. The resulting abnormal chromosomes interfere with normal control of cell division, so that affected cells multiply uncontrollably or are resistant to normal cell death, resulting in leukemia.

Classification

Leukemias are grouped into four main types:

  • Acute lymphocytic leukemia

  • Acute myelocytic leukemia

  • Chronic lymphocytic leukemia

  • Chronic myelocytic leukemia

The types are defined according to how quickly they progress and the type and characteristics of the white blood cells that become cancerous. Acute leukemias progress rapidly and consist of immature cells. Chronic leukemias progress slowly and consist of more mature cells. Lymphocytic leukemias develop from cancerous changes in lymphocytes or in cells that normally produce lymphocytes. Myelocytic (myeloid) leukemias develop from cancerous changes in cells that normally produce neutrophils, basophils, eosinophils, and monocytes.

Complications

Leukemia cells ultimately occupy the bone marrow, replacing or suppressing the function of cells that develop into normal blood cells. This interference with normal bone marrow cell function can lead to inadequate numbers of red blood cells (causing anemia), white blood cells (increasing the risk of infection), and platelets (increasing the risk of bleeding). Leukemia cells may also invade other organs, including the liver, spleen, lymph nodes, testes, and brain.

Causes

The cause of most types of leukemia is not known. Exposure to radiation, to some types of chemotherapy, or to certain chemicals (such as benzene) increases the risk of developing some types of leukemia, although leukemia develops only in a very small number of such people. Certain hereditary disorders, such as Down syndrome and Fanconi anemia, increase the risk as well. In some people, leukemia is caused by certain abnormalities of the chromosomes. A virus known as human T lymphotropic virus 1 (HTLV-1), which is similar to the virus that causes AIDS, is strongly suspected of causing a rare type of lymphocytic leukemia called adult T-cell leukemia. Infection with the Epstein-Barr virus (which also causes mononucleosis) has been associated with an aggressive form of lymphocytic leukemia called Burkitt leukemia.

Treatment

Many leukemias can be effectively treated, and some can be cured.

The complications of leukemia may also need treatment. People may need blood transfusions if leukemia has caused severe anemia. They may need antibiotics if infections develop. If bleeding occurs, they may need platelet transfusions.

When leukemia is under control, the number of abnormal cells in the bone marrow is not increased and people are said to be in remission. If leukemia cells appear again, people are said to have a relapse. For some people in relapse, quality of life eventually deteriorates, and the potential benefit for further treatment may be extremely limited. Keeping people comfortable may become more important than trying to modestly prolong life. Affected people and their family members must be involved in these decisions. Much can be done to provide compassionate care, relieve symptoms (see Treatment Options at the End of Life), and maintain dignity.

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