What is leukemia?
The term leukemia comes from the Greek words for "white" (leukos) and "blood" (haima). Leukemia is a cancer (an abnormal growth of cells) of the blood and bone marrow. Unlike other cancers, leukemia does not produce a mass (tumor), but results in the overproduction of abnormal white blood cells.
Leukemia begins in the immature or developing cells of the bone marrow, 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 grow in number, the leukemic cells also interfere with the production of other blood cells.
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 4 main forms of leukemia are:
- Acute lymphocytic leukemia (ALL)
- Chronic lymphocytic leukemia (CLL)
- Acute myelogenous leukemia (AML)
- Chronic myelogenous leukemia (CML)
In addition, there also are various subtypes of leukemia. Subtypes of lymphocytic leukemia include hairy cell, Waldenstrom’s macroglobulinemia, prolymphocytic, and lymphoma cell leukemia. Among the subtypes of myelogenous leukemia are myelogenous, promyelocytic, monocytic, erythroleukemia, and megakaryocytic leukemia.
What causes leukemia?
Leukemia results when the DNA of a single cell in the bone marrow becomes damaged. This is called a mutation and changes 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.
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:
- Anemia: Anemia is caused by having a lower than normal number of red blood cells, which slows down the delivery of oxygen to the body's organs and muscles. A person with anemia may have a pale complexion and may tire easily and have little energy.
- Easy bruising or bleeding: People with leukemia may bleed from their gums or noses, or may find blood in their stool or urine. Bruises may develop from very minor bumps. Small spots of discoloration — called petechiae — may form under the skin.
- Susceptibility to infections: Because leukemia affects the body's infection-fighting cells, a person with this cancer may develop infections, such as a sore throat or bronchial pneumonia. A headache, low-grade fever, mouth sores or skin rash may accompany the infection.
- Swollen lymph nodes: Lymph nodes are small, bean-sized structures that contain clusters of lymphocytes. In a person with leukemia, abnormal lymphocytes may collect in lymph nodes in the throat, armpits or groin, causing the lymph nodes to become enlarged.
- General loss of well-being: Other symptoms of leukemia include loss of appetite and weight, discomfort under the left lower ribs (caused by a swollen spleen, also from a collection of abnormal lymphocytes) and a feeling of weakness or fatigue all the time. In some cases, a person with leukemia may get a fever that lasts for more than 1 to 2 weeks and may have night sweats.