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. 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.

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.

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's syndrome, 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 has been associated with an aggressive form of lymphocytic leukemia called Burkitt's leukemia.

Treatment

Many leukemias can be effectively treated, and some can be cured. When leukemia is under control, 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 Death and Dying: Quantity Versus Quality), and maintain dignity.

Myelodysplastic Syndromes In myelodysplastic syndromes, a line of identical cells (clone) develops and occupies the bone marrow. These abnormal cells do not grow and mature normally. The cells also interfere with normal bone marrow function, resulting in deficits of red blood cells, white blood cells, and platelets. In some people, red blood cell production is predominantly affected. Myelodysplastic syndromes occur most often in people older than 50 years. Men are more than twice as likely as women to be affected. The cause is usually not known. However, in some people, exposure of bone marrow to radiation therapy or certain types of chemotherapy drugs may play a role. Symptoms develop very slowly. Fatigue, weakness, and other symptoms of anemia are common. Fever due to infections may develop if the number of white blood cells decreases. Easy bruising and abnormal bleeding can result if the number of platelets drops. A myelodysplastic syndrome may be suspected when people have unexplained persistent anemia, but diagnosis requires a bone marrow biopsy. People with myelodysplastic syndromes often need transfusions of red blood cells. Platelets are transfused only if people have uncontrolled bleeding, or if surgery is needed and the number of platelets is low. People who have very low numbers of neutrophils—the white blood cells that fight infection—may benefit from intermittent injections of a special type of protein called a colony-stimulating factor. The drugs azacitidine and deoxyazacitidine can reduce the need for transfusions and prolonging survival, but they do not cure myelodysplastic syndromes. Allogeneic stem cell transplantation cures a few patients. Although myelodysplastic syndromes are thought to be a type of leukemia, they progress gradually, over a period of several months to years. In 10 to 30% of people, a myelodysplastic syndrome transforms into acute myelocytic leukemia (AML). Treatment with chemotherapy during the early stages of a myelodysplastic syndrome does not help prevent transformation to AML. If transformation to AML occurs, chemotherapy may be helpful, but the AML is unlikely to be curable.

Last full review/revision June 2008 by Emil J. Freireich, MD