Article updated and reviewed by Corey Cutler, MD MPH FRCP(C), Instructor in Medicine, Harvard Medical School, Dana-Farber Cancer Institute on May 11, 2005.
Leukemia is a malignant disorder (a form of cancer) that involves the bone marrow and blood systems. Leukemia results in the uncontrolled growth of abnormal (leukemic) white blood cells. As a result of the uncontrolled growth of leukemic cells in the bone marrow, there is inadequate space in the bone marrow for normal blood production (hematopoiesis) to occur. The lack of normal blood growth results in the lack of normal white blood cells (increasing the risk of infection), the lack of red blood cells (resulting in fatigue, weakness, and anemia) and the lack of normal platelet production (increasing the risk of bleeding).
There are many different types of leukemia. Each of these types may appear with some, none, or all of the symptoms or signs described below.
The term leukemia, which is derived from Greek, literally means "white blood." The bone marrow may become severely impaired and unable to maintain production of sufficient levels of red blood cells and platelets. At the same time, white blood cell production becomes so rapid that these cells do not reach the level of maturity necessary to perform their infection-fighting functions.
Leukemic cells infiltrate all the major organs of the body, sometimes causing these organs to malfunction or fail. The kidneys may become impaired. The liver and spleen may become enlarged.
Normally, the spleen acts as a filter for the blood, screening out aging red cells and platelets. When the spleen becomes enlarged, it can actually start doing its job too well, removing perfectly healthy red cells and platelets, further reducing the number of these already scarce cells.
As leukemia progresses, the entire blood system may become flooded with immature blast cells. If this disease is left untreated, a person with leukemia becomes increasingly susceptible to fatigue, excessive bleeding and infections until, finally, the body becomes virtually defenseless, making every minor injury or infection very serious.
Leukemia may be fatal. People may die from internal bleeding which would have been prevented by the platelets. Or, more often, they may die from infections which start with a virus or bacteria that would ordinarily have been wiped out by healthy white blood cells. The exact course leukemia takes, and the speed with which it takes that course, varies with the type and age of the white cells initially affected.
The cause of leukemia in most circumstances is not known. There are very few hereditary forms of leukemia. Some risk factors for leukemia may include exposure to toxins, chemicals, drugs, or radiation.
There are two major subtypes of leukemia: (i) lymphocytic leukemia, which involves white blood cells of the lymphoid subtype, and (ii) myelogenous leukemia, which involves white blood cells of the myeloid subtype. Both lymphoid and myeloid cells are critical components of the mature immune system.
Each of these two lineages of leukemia can occur in acute or chronic forms. As the names imply, acute leukemias occur quickly and can be rapidly life-threatening, unless treated urgently. On the other hand, chronic leukemias develop over longer periods of time and are associated with better survival than the acute leukemias. Based on the two lineages of leukemia and the two respective subtypes, there are four important types of leukemia: ALL (Acute Lymphoblastic Leukemia), AML (Acute Myelogenous Leukemia), CLL (Chronic Lymphocytic Leukemia), and CML (Chronic Myelogenous Leukemia). Within each of these four major subtypes of leukemia, there are even further subdivisions that can be made, specific for each of the four subtypes. There are a number of other less common forms of leukemia as well.
The diagnosis of leukemia is made based on a compatible clinical history and a confirmatory laboratory investigation. A complete blood count (CBC) is almost always abnormal, with leukemic cells often found in the peripheral circulation. Often, the total white blood cell count is elevated, and the red blood cell count is depressed (anemia) as is the platelet count (thrombocytopenia).
The identification of the various forms of leukemia is based on the appearance of the leukemic cells in the blood and the bone marrow, the cell surface characteristics of the leukemic cells (based on immunohistochemistry and flow cytometry studies), as well as the presence of certain specific chromosomal abnormalities identified within the leukemic cells.
Although suspected by medical history or physical examination, leukemia may be diagnosed incidentally when blood tests or radiological studies are performed for other indications. A bone marrow biopsy may be recommended by your physician.
Therapy of leukemia is dependent on the subtype of leukemia and the clinical condition of the patient. Some forms require no therapy for extended periods of time, while others require urgent medical attention. Leukemia is treated mainly with chemotherapy, although radiotherapy and biological therapy can be used in certain subtypes of leukemia. Bone marrow transplantation may be recommended for some types of leukemia.
Editorial review provided by VeriMed Healthcare Network.