Chronic Lymphocytic Leukemia
Chronic lymphocytic leukemia is a disease in which mature lymphocytes become cancerous and gradually replace normal cells in lymph nodes.
More than three fourths of the people who have chronic lymphocytic leukemia (CLL) are older than 60, and the disease does not occur in children. This type of leukemia affects men 2 to 3 times more often than women. CLL is the most common type of leukemia in North America and Europe. It is rare in Japan and Southeast Asia, which indicates that heredity plays some role in its development.
The number of cancerous mature lymphocytes increases first in the blood and lymph nodes. They then spread to the liver and spleen, both of which begin to enlarge. Cancerous lymphocytes also invade the bone marrow, where they crowd out normal cells, resulting in a decreased number of red blood cells and a decreased number of normal white blood cells and platelets in the blood. The level of antibodies, proteins that help fight infections, also decreases. The immune system, which ordinarily defends the body against foreign organisms and substances, sometimes becomes misguided, reacting to and destroying normal body tissues. This misguided activity can sometimes result in the destruction of red blood cells and platelets.
In 95% of cases, CLL is a disorder of B lymphocytes (B cells (see Section 16, Chapter 183)). There are other types of CLL other than B-cell CLL. Hairy cell leukemia, a slow-growing uncommon type of B-cell leukemia, produces a large number of abnormal white blood cells with distinctive hairlike projections that are visible under a microscope. T-cell leukemia (leukemia of T lymphocytes) is much less common than B-cell leukemia. Sézary syndrome is a rare type of T-cell leukemia in which cancerous T lymphocytes that start as a skin cancer called mycosis fungoides (see Section 14, Chapter 177) grow and divide more rapidly and enter the bloodstream, becoming leukemia cells.
Symptoms and Diagnosis
In early stages of CLL, most people have no symptoms, and the disease is diagnosed only because of an increased white blood cell count. Later symptoms may include enlarged lymph nodes, fatigue, loss of appetite, weight loss, shortness of breath when exercising, and a sense of abdominal fullness resulting from an enlarged spleen.
As CLL progresses, the person may appear pale and bruise easily. Bacterial, viral, and fungal infections generally do not occur until late in the course of the disease.
Sometimes the disease is discovered accidentally when blood counts ordered for some other reason show an increased number of lymphocytes. A bone marrow biopsy is usually not needed to confirm the diagnosis because specialized tests to characterize the lymphocytes can be performed on the cells in the blood. Blood tests also may show that the person has a decreased number of red blood cells, platelets, and antibodies.
Prognosis
Most types of CLL progress slowly. A doctor determines how far the disease has progressed (staging) to predict the person's survival time. Staging is based on factors such as the number of lymphocytes in the blood and bone marrow, size of the spleen and liver, presence or absence of anemia, and platelet count.
People who have B-cell leukemia often survive 10 to 20 years or longer after the diagnosis is made and usually do not need treatment in the early stages. People who are anemic or who have a low number of platelets need more immediate treatment and have a less favorable prognosis. Usually, death occurs because the bone marrow can no longer produce a sufficient number of normal cells to carry oxygen, fight infections, and prevent bleeding. The prognosis for people who have T-cell leukemia is usually worse.
For reasons probably related to changes in the immune system, people who have CLL are more likely to develop other cancers, such as skin or lung cancers. CLL can also transform into a more aggressive type of lymphoma.
Treatment
Because CLL progresses slowly, many people do not need treatment for years--until the number of lymphocytes begins to increase, the lymph nodes begin to enlarge, or the number of red blood cells or platelets decreases.
Drugs used to treat the leukemia itself help relieve symptoms and eliminate enlarged lymph nodes and spleen but do not cure the disease. For B-cell CLL, initial drug treatment includes alkylating drugs such as chlorambucil, which kill cancer cells by interacting with their DNA, or a drug called fludarabine, which is given intravenously. Either treatment can control CLL for months to many years and can be used again with success when the leukemia regrows. Eventually CLL becomes resistant to these drugs, and sometimes experimental treatments with other drugs or monoclonal antibodies (such as alemtuzumab) are considered. For hairy cell leukemia, 2-chlorodeoxyadenosine and pentostatin are highly effective and can control the disease for more than 15 years.
Anemia due to a decreased number of red blood cells is treated with blood transfusions and occasionally with injections of erythropoietin or darbepoietin (drugs that stimulate red blood cell formation). Low platelet counts are treated with platelet transfusions, and infections are treated with antibiotics. Radiation therapy is used to shrink enlarged lymph nodes or an enlarged liver or spleen if the enlargement is causing discomfort and chemotherapy is ineffective.
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