Introduction

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 and become cancerous (malignant), resulting in leukemia. Leukemia cells ultimately occupy the bone marrow, replacing or suppressing the function of cells that develop into normal blood cells. Leukemia cells may also invade other organs, including the liver, spleen, lymph nodes, testes, and brain.

Leukemias are grouped into four main types--acute lymphocytic leukemia, acute myelocytic leukemia, chronic lymphocytic leukemia, and chronic myelocytic leukemia--according to how quickly they progress and the type of cell that becomes cancerous. Acute leukemias progress rapidly; chronic leukemias progress slowly. 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.

The cause of most types of leukemia is not known. Exposure to radiation or to some types of chemotherapy increases the risk of developing some types of leukemia, although leukemia develops in a very small number of people receiving such treatments. Certain hereditary disorders, such as Down syndrome and Fanconi's syndrome, increase the risk as well. A virus known as HTLV-I (human T-cell lymphotropic virus type I), 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 has been associated with an aggressive form of lymphocytic leukemia called Burkitt's leukemia.

Many leukemias can be effectively treated; some can be cured. When a leukemia is under control, the person is said to be in remission. If leukemia cells appear again, the person is said to have a relapse. For some people in relapse, quality of life may eventually deteriorate, and the potential benefit for further treatment may be extremely limited. Keeping the person comfortable may become more important than trying to modestly prolong his or her life. The person and family members must be involved in these decisions. Much can be done to provide compassionate care, relieve symptoms (see Section 1, Chapter 8), and maintain the person's dignity.

See the sidebar Myelodysplastic Syndromes.