Leukemia is the name of a group of cancers that affect white blood cells. It takes its name from the abnormally high numbers of white blood cells found in patients' blood before treatment. It is not a single disease; there are four major types of leukemia, two that are considered acute (they worsen rapidly) and two that are chronic (they progress slowly). These four types are:
- Chronic lymphocytic leukemia (CLL). A lymphocytic leukemia is one in which the cancer affects white blood cells (WBCs) called lymphocytes. The abnormal but relatively mature cells multiply, keeping normal cells from doing their job of fighting infections.
CLL is related to another type of cancer called lymphoma, which is a cancer that affects the lymphatic system. CLL is a common adult leukemia; it progresses slowly and many patients feel well for years without treatment.
- Chronic myeloid leukemia (CML). A myeloid leukemia is one that affects bone marrow cells that normally produce platelets (small cells that affect the blood's ability to clot), and a few types of white blood cells called neutrophils. CML is associated with an abnormality in chromosome 9 called the Philadelphia chromosome. This abnormality occurs when a portion of the genetic material in chromosome 9 is exchanged with a portion of the genetic material in chromosome 22. Ninety-five percent of patients with CML have this genetic alteration. Like CLL, CML is a slowly developing form of leukemia; patients diagnosed with it may have few or no symptoms for months or years before the disease grows worse.
- Acute lymphocytic leukemia (ALL). ALL is the most common type of leukemia in young children and can be rapidly fatal if not treated. In ALL, the patient's bone marrow produces a large number of immature malignant lymphocytes that crowd out healthy blood cells, both red and white. Children with ALL are vulnerable to infection and easy bleeding. The abnormal WBCs can also collect in certain areas of the body, including the central nervous system and spinal cord. This buildup can cause such symptoms as severe headaches, difficulty breathing, a swollen liver and spleen, and dizziness.
- Acute myeloid leukemia (AML). AML is caused by the rapid multiplication of abnormal and immature neutrophils or similar cells that build up within the bone marrow and interfere with the production of normal cells. It worsens quickly if not treated, but it may respond well to therapy, at least in the beginning. Unfortunately, many patients with AML suffer relapses.
There are about 31,000 cases of leukemia diagnosed in the United States each year, 2,000 in children and 29,000 in adults. Of the four major
types of leukemia, about 14,000 cases of CLL are diagnosed each year, almost all of them in adults over fifty-five; 4,400 cases of CML, mostly in adults; 3,800 cases of ALL, almost all in children; and 11,000 cases of AML, which affects both adults and children.
Two-thirds of patients with CLL are men; ALL is slightly more common in men and boys than in women and girls; and about 60 percent of patients with AML are men.
ALL is more common in Italy, the United States, Switzerland, and Costa Rica than in other countries; AML is more common in Caucasians in the United States than in other ethnic groups. CLL is more common in Jewish people of Eastern European descent than in other ethnic groups.
The causes of leukemia are not completely understood. What is known is that there are several risk factors for these forms of cancer.
- Exposure to high levels of radiation, most often from radiation used to treat other forms of cancer or from nuclear accidents.
- Exposure to certain chemicals, such as benzene or formaldehyde. This type of exposure is most likely to affect adults.
- Chemotherapy for other forms of cancer. Adults treated with certain types of cancer-killing medications may develop leukemia later on.
- Down syndrome. People with this particular genetic disorder have higher rates of leukemia than people in the general population.
- Chromosomal abnormalities such as the Philadelphia chromosome.
It is important to keep in mind, however, that most people with these risk factors do not develop leukemia, and that many people who do suffer from leukemia have none of these risk factors.
The early symptoms of leukemia may develop gradually rather than suddenly and are often mistaken for the symptoms of other diseases. About 20 percent of patients with chronic leukemia do not have any noticeable symptoms at the time they are diagnosed—most often as the result of a routine blood test. Common symptoms of leukemia include:
- Fever and night sweats
- Feeling tired much of the time
- Getting frequent colds and other infections
- Pain in the bones or joints
- Swelling or pain in the abdomen from enlargement of the spleen
- Cuts or sores taking an unusually long time to heal
- Swelling of the lymph nodes in the neck or armpit
- Unintentional weight loss
- Soft tissue bruising easily, with frequent purple areas or pinpoint bruises under the skin
- Gums and open cuts bleeding easily
- Shortness of breath
- Nausea or vomiting
- In some cases, confusion, dizziness, seizures, or blurred vision
The diagnosis of leukemia is complicated by the fact that most of its early symptoms are nonspecific; that is, they occur in many other diseases. The diagnosis is made by a combination of blood tests to check the patient's white blood cell number and kind, followed by a bone marrow biopsy. To do the biopsy, a hematologist (doctor who specializes in the diagnosis and treatment of blood disorders) draws a sample of bone marrow (usually from the hip bone) through a needle after the patient has been given a local anesthetic. The biopsy is necessary to confirm the diagnosis because some diseases other than leukemia can cause an abnormally high number of white blood cells, and some leukemias can only be found in early stages in the bone marrow.
In some cases the doctor will also order a chest x ray or a spinal tap to check for signs of leukemia. In a spinal tap, a small amount of cerebrospinal fluid is removed from the spinal column through a needle. It is done to see whether the disease has spread to the brain or spinal cord.
Treatment for leukemia varies according to the type of disease:
- CLL: Low-grade forms of CLL may not be given any form of treatment because patients do not benefit from therapy in the early stages of the disease. Patients are usually treated when their RBC count or platelet count starts to drop, the lymph nodes become painful, or the number of abnormal WBCs starts to rise sharply. Patients are usually treated with combination chemotherapy; younger patients sometimes benefit from bone marrow transplantation.
- CML: There are several anticancer drugs that can be used to treat CML, but in recent years the standard treatment is a drug called Gleevec, which has relatively few side effects and can be taken by mouth at home. About 90 percent of patients can be maintained on Gleevec for five years without the disease becoming worse. If the drug stops working, bone marrow transplantation is an option; however, the procedure is risky as 30 percent of CML patients die shortly after the operation.
- ALL: Treatment of ALL is focused on preventing the disease from spreading into the central nervous system. It generally has four phases: a beginning phase of chemotherapy to stop the production of abnormal WBCs in the bone marrow; a second phase of medication therapy to eliminate remaining leukemia cells; a third phase of radiation or chemotherapy to prevent the disease from spreading to the brain and spinal cord; and maintenance treatment with chemotherapy to prevent the disease from recurring. ALL can also be treated by bone marrow transplantation.
- AML: AML is treated primarily by chemotherapy in two stages: an induction phase in which the patient is given drugs to reduce the number of cancerous blood cells to an undetectable level; and a second or consolidation phase to eliminate any remaining abnormal cells.
Treatment for leukemia also includes antibiotics to help fight infections when needed, since patients with this type of cancer are vulnerable to infection. The doctor will also provide advice about nutrition and refer the patient to a dietitian if necessary to make sure that the patient is eating a healthy diet and is not losing weight.
Although chemotherapy is the mainstay of treatment for leukemia, in some cases the doctor may recommend surgery to remove the spleen if it has become enlarged. This operation is usually done to control pain and avoid pressure on other organs in the patient's abdomen.
The prognosis of leukemia depends on the specific type. In general, females have a better prognosis than males.
- CLL: The five-year survival rate is 75 percent.
- CML: The five-year survival rate is 90 percent.
- ALL: Survival rates vary depending on the patient's age. The five-year survival rate is 85 percent for children but only 50 percent for adults.
- AML: The five-year survival rate is 40 percent.
There is no known way to prevent leukemia because the causes of this group of cancers are still not known.
Leukemia is one type of cancer in which survival rates have increased dramatically since the 1960s. In 1960 the overall five-year survival rate for all types of leukemia was about 14 percent; it is over 50 percent as of the early 2000s.
Cancer research in general is a rapidly expanding field. Many new medical centers devoted entirely to cancer research and treatment have been established across the United States. Doctors are testing new approaches to cancer treatment as well as new anticancer drugs, doses, and treatment schedules. Other researchers are working on improving the technique of bone marrow transplantation as a way to treat leukemia, as well as improved methods of diagnosing the disease.
SEE ALSO Down syndrome; Lymphoma
WORDS TO KNOW
Acute: Referring to a disease or symptom that is severe or quickly worsens.
B cell: A type of white blood cell produced in the bone marrow that makes antibodies against viruses.
Bone marrow: The soft spongy tissue inside the long bones of the body where blood cells are formed.
Chronic: Referring to a disease or symptom that goes on for a long time, tends to recur, and usually gets worse slowly.
Hematologist: A doctor who specializes in diagnosing and treating disorders of the blood.
Lymphocyte: The medical term for white blood cells. A lymphocytic anemia is one that affects the cells in the bone marrow that give rise to white blood cells.
Lymphoma: A type of cancer that affects the lymphatic system.
Myeloid: Relating to bone marrow.
Philadelphia chromosome: A genetic abnormality in chromosome 9 associated with CML. Its name comes from the location of the University of Pennsylvania School of Medicine, where it was discovered in 1960.
Platelet: A type of small blood cell that is important in forming blood clots.
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National Library of Medicine (NLM). Leukemia. Available online at http://www.nlm.nih.gov/medlineplus/tutorials/leukemia/htm/index.htm (accessed on June 6, 2008). This is an online tutorial with voiceover; viewers have the option of a self-playing version, a text version, or an interactive version with questions.