The term leukemia comes from the Greek words for "white" (leukos) and "blood" (haima). Leukemia is a malignant disease, or cancer (an abnormal growth of cells) of the blood and bone marrow. Unlike other cancers, leukemia does not produce a mass, called a tumor, but results in the overproduction of abnormal white blood cells.
Leukemia begins in the immature, or developing, cells of the bone marrow, which is the soft, spongy tissue found in the central cavities of bones. The bone marrow produces all types of blood cells: red blood cells that carry oxygen and other materials to the tissues of the body, white blood cells that fight infection, and platelets that help the blood clot. Hundreds of billions of new blood cells are produced in the bone marrow each day, providing the body with a constant supply of fresh, healthy cells.
In a patient with leukemia, many of the white blood cells produced in the bone marrow do not mature normally. These abnormal cells, called leukemic cells, are unable to fight infection the way healthy white cells can. As they accumulate, the leukemic cells also interfere with the production of other blood cells. Eventually, the body has too few red cells for supplying oxygen to the body’s tissues, too few platelets for proper clotting and too few healthy white cells for fighting infection. As a result, people with leukemia are at risk for bruising, bleeding and infections.
How common is leukemia?
Leukemia often is considered a disease of children, yet it actually affects far more adults. In fact, the frequency of the disease increases with age. Leukemia is more common in men than in women, and more common in Caucasians than in African-Americans. Almost 30,000 cases are diagnosed in the United States each year.
What are the types of leukemia?
There are many types of leukemia, which are classified by the specific type of white blood cell involved. White blood cells include neutrophils and monocytes, which ingest (eat) bacteria and other germs; eosinophils and basophils, which are involved in allergic reactions; and lymphocytes, which play a key role in our body’s immune system.
The main types of leukemia are myelogenous and lymphocytic, and each type has an acute (rapidly progressing) and a chronic (slowly progressing) form. Acute leukemia mainly affects cells that are immature, or not fully developed, preventing them from maturing and functioning normally. Chronic leukemia develops more slowly, so that the body still has some healthy cells available to fight infection.
The four main forms of leukemia are:
In addition, there also are various subtypes of leukemia. Subtypes of lymphocytic leukemia include hairy cell, macroglobulinemia, prolymphocytic and lymphoma cell leukemia. Among the subtypes of myelogenous leukemia are myeloblastic, promyelocytic, monocytic, erythroleukemia and megakaryocytic leukemia.
What are the symptoms of leukemia?
In many cases, people in the early stages of leukemia have no obvious symptoms. When symptoms do appear, they may include:
What causes leukemia?
Leukemia results when the DNA of a single cell in the bone marrow becomes damaged, called a mutation, thereby changing the cell’s ability to develop and function normally. Further, all cells that arise from that initial cell also have the mutated DNA. What causes the damage to the DNA in the first place, however, is still not known. (DNA is the material in a cell that holds the instruction codes for the cell’s growth and function. Segments of DNA make up genes, which are arranged on larger structures called chromosomes.) Scientists have been able to locate changes in certain chromosomes of patients diagnosed with different types of leukemia.
Although the exact cause of the DNA mutation that leads to leukemia is unknown, scientists have discovered certain factors that may put a person at higher risk for developing a form of the disease. For example, very high doses of radiation, exposure to the chemical benzene and exposure to certain chemotherapy drugs may increase the risk of developing AML, ALL or CML.
People with certain genetic disorders, such as Down syndrome, may be at higher risk for AML.
Further, a specific genetic abnormality—called the Philadelphia chromosome (Ph) after the city in which it was first identified—has been found in the marrow and blood cells of people with CML.
How is leukemia diagnosed?
Because chronic leukemia shows no obvious symptoms in the early stages, the disease may be diagnosed during a regular physical examination or as a result of routine blood tests. If a patient has enlarged lymph nodes, swollen gums, an enlarged liver or spleen, significant bruising or a small pinpoint rash, the doctor may suspect leukemia. Many patients initially just feel overall severe fatigue or flu-like symptoms which linger and do not improve.
To diagnose leukemia, the doctor must examine cells from the blood and, in most cases, the bone marrow. An initial blood test (complete blood count [CBC]) showing an abnormal white cell count may indicate the need for a bone marrow biopsy to confirm the diagnosis and to identify the specific type of leukemia. During this procedure, the doctor removes a sample of bone marrow tissue (biopsy) from a pelvic bone and tests the sample for cancer cells. The cells also are examined for chromosomal abnormalities. This is called a cytogenetics analysis (cyto=cell).
How is leukemia treated?
Treatment varies with the type and stage of the disease. For acute leukemia, the immediate goal of treatment is remission, which means no more cancerous cells can be detected and the bone marrow appears normal. The patient undergoes aggressive chemotherapy (the use of drugs to kill cancer cells) in a hospital for about 4 weeks. Since acute leukemia patients have extremely low counts of healthy blood cells, they usually are given transfusions of red blood cells and platelets. They also receive drugs to combat infection, and to reduce nausea and vomiting that may occur as side effects of the chemotherapy.
What is the prognosis for people with leukemia?
The rate of leukemia has not changed much since the 1950s, but more people are surviving longer, thanks mainly to advances in chemotherapy. ALL (childhood leukemia), for example, represents one of the most dramatic success stories in cancer treatment. Almost 90 percent of children diagnosed with the disease attain remission, and more than half are cured completely. The 5-year survival rate for all patients with ALL has risen from 4 percent in the 1960s to more than 50 percent in the 1990s.
Adult patients treated for ALL have an 80 percent to 90 percent chance of attaining remission; about 40 percent of those who do so survive at least another five years, with a chance of a full cure. Patients treated for AML have a 60 percent to 70 percent chance of remission; about 20 percent of those survive at least three years, with a possibility of a full cure.
Can leukemia be prevented?
At this time, there is no known way to prevent leukemia.
When should I see a physician?
Call your doctor if:
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