Overview
Healthy blood cells go through an orderly life cycle. They are generated in the bone marrow, they mature and develop into specialized cells, and they then carry out specific jobs in the body, such as fighting infection or carrying oxygen. The cells eventually die, leaving room for the next generation. When leukemia occurs, for some reason white blood cells fail to go through this normal cycle. In some cases, these cells remain immature and are unable to carry out their normal duties. They are commonly known as blasts. In other cases, the cells look mature but still do not function properly. In addition to not working properly, the malfunctioning cells can accumulate in the body. Some reproduce themselves over and over, producing a very large number of diseased cells in the blood and bone marrow. Others, because they live an abnormally long time, build up and destroy tissue in the bone marrow, spleen, or lymph nodes, or crowd the bone marrow and disrupt the production of other blood cells. These malfunctioning cells can lead to a wide variety of symptoms, including infections, anemia, and pain and swelling in bones and joints.
Leukemia, unlike many other types of cancer, does not usually result in a solid mass of cells or tumor.
Four Primary Types of Leukemia
Leukemia can arise from any of the types of white blood cells. When diagnosing leukemia, one basic consideration is which type of cell is involved.
- Lymphocytic leukemia develops in cells in the lymphocytic cell line -- the line that produces T-cell lymphocytes and B-cell lymphocytes.
- Myelogenous leukemia arises in cells in the myeloid cell line -- the line that produces the granulocytes and monocytes.
- Another consideration is whether the leukemia is acute or chronic.
- Acute leukemia occurs when the affected blood cells remain in a very immature stage -- as blasts. They never progress beyond this primitive state and don't function properly. Acute leukemia usually is a rapidly progressing disease. Most children who have leukemia are diagnosed with an acute form of the disease.
- Chronic leukemia is diagnosed when most of the affected cells are more mature; they do not function completely normally, but they can perform some of their duties. Some blasts are present as well, but not as many as in acute forms of the disease. Chronic leukemia progresses more slowly than acute leukemia.
Thus, there are four main types of leukemia.
- Acute lymphocytic leukemia (ALL)
- Acute myelogenous leukemia (AML)
- Chronic lymphocytic leukemia (CLL)
- Chronic myelogenous leukemia (CML)
In the case of acute leukemia, on rare occasions doctors are unable to determine if the disease is of the lymphocytic or the myelogenous type. The disease is then called acute unclassifiable leukemia, or AUL. In some cases, the cells show characteristics of both types; these may be classified as ALL with myeloid markers, AML with lymphoid markers, or biphenotypic leukemia.
Of the 30,800 people who will be diagnosed with leukemia this year, 2,700 will be children.
- ALL will be diagnosed in about 3,800 people. Of these, 2,000 will be children.
- CLL will be diagnosed in 7,000 people, mostly adults.
- AML will be diagnosed in 10,600 people, both children and adults.
- CML will be diagnosed in 4,400 people, primarily adults.
Other types of leukemia will be found in 5,000 people.
Leukemia Symptoms
The overabundance of malfunctioning white blood cells can affect the body in many different ways, resulting in a number of symptoms. For example, if leukemic cells prevent the proper development of red blood cells, the patient may develop anemia. This can cause fatigue and shortness of breath. If the disease prevents the development of platelets, bleeding and bruising may develop. A lack of functioning white blood cells can lead to infections. Leukemic cells can also collect in places and cause swelling and other problems. In many people, the first sign of leukemia is a nonspecific feeling of not being well -- they may simply feel fatigued or be losing weight for no apparent reason. Some people won't experience any symptoms at all. Other possible symptoms include:
- anemia
- shortness of breath
- unusual bleeding and bruises
- slow healing of cuts
- mid-cycle or heavy menstrual bleeding
- small red spots under the skin, known as petechiae
- headaches
- vision problems
- seizures or confusion
- vomiting
- enlarged lymph nodes
- numerous minor infections, such as skin, ear, or urinary tract infections
- fever, chills, or flu-like symptoms
- sore throat
- loss of appetite
- swollen liver, spleen, or testicles
- swollen or bleeding gums
- night sweats
Diagnosis
If leukemia is suspected, the doctor will do a physical examination to check for swollen organs or lymph nodes and to look for any other signs of disease.
Laboratory tests are also necessary. Blood tests are done to examine the blood under a microscope to look for changes in the numbers and types of blood cells. Samples of bone marrow tissue will be examined for abnormalities. Other tests, such as genetic studies and imaging tests, may also be required. You will find more information under Detection and Diagnosis.
Causes
What causes leukemia is mostly a mystery. Only a few factors have been identified that are known to increase a person's risk for the disease. Known causes include exposure to very high doses of radiation or to the chemical benzene, and cigarette smoking. People who have been treated for cancer with certain chemotherapy drugs are also more likely to develop leukemia in later years. Some cases of childhood leukemia might also be the result of the child's exposure to infectious or toxic substances while in the womb or during early childhood. Some common genetic disorders, such as Down syndrome and Fanconi anemia, are known to give a person a higher risk of developing leukemia. Many cases of leukemia are also linked to another genetic error, an abnormality known as the Philadelphia chromosome. This abnormality, called a translocation, occurs when two chromosomes swap pieces of genetic material. In this case, chromosome 22 is exchanging material with chromosome 9. The altered genetic material now found on chromosome 22 is called the BCR-ABL fusion gene. It tells the body to produce a protein that somehow triggers the growth of leukemia cells. In most cases, scientists don't know why the chromosome is altered in the first place.
These factors, however, account for only a small percentage of the leukemia cases. In most cases scientists just don't know what causes someone to develop the disease. It is important to keep in mind, too, that even if someone does have a known risk factor, such as smoking, it is impossible to say that that is what caused the disease.
Hairy Cell Leukemia
A less common form is known as hairy cell leukemia, or HCL. It is a chronic type of leukemia that accounts for about 2 percent of all leukemia cases. HCL is more common in men; the average age at diagnosis is 54. HCL often resembles chronic lymphocytic leukemia or small lymphocytic lymphoma. Like CLL, it arises from an abnormality in the lymphocyte cell line. The abnormal cells have tiny projections on them, making them look hairy. There may be no symptoms for several years, but when they do occur symptoms may include a greatly enlarged spleen, anemia, and frequent infections. About ten percent of people diagnosed with HCL never need any treatment. Many others require no treatment other than careful monitoring for quite some time. Others who are more symptomatic may be treated with removal of the spleen or with the chemotherapy drugs cladribine or pentostatin. Another option is treatment with the drug interferon alpha. In most cases the disease is easily controlled.
Acute Promyelocytic Leukemia (APL)
Acute promyelocytic leukemia is classified as a subtype of acute myelogenous leukemia (ALM). It is distinct, however, because stem cell progression and differentiation into neutrophils stops during the promyelocyte stage. Because the cell growth is arrested, there is an abnormal increase in promyelocytes, which then crowd out normal cells in the bone marrow. This leads to lowered red and white blood cell and platelet counts. Resulting symptoms are anemia, which produces feelings of fatigue and weakness, and easy bruising and bleeding. Patients are at increased risk of infection due to lowered white blood cell counts.
