Leukemia

Leukemia is cancer of your body's blood-forming tissues, including the bone marrow and lymph system. The word leukemia means "white blood" in Greek. The disease usually starts in the white blood cells.

Under normal circumstances, your white blood cells are potent infection fighters. These cells normally grow and divide in an orderly, controlled way, as your body needs them. But leukemia disrupts this process.

In people with leukemia, the bone marrow produces a large number of abnormal white blood cells. They look different from normal blood cells and don't function properly. Eventually, they block production of normal white blood cells, impairing the ability to fight off infection. Leukemia cells also crowd out other types of blood cells produced by the bone marrow, including red blood cells, which carry oxygen to tissues throughout the body, and platelets, which help form blood clots that control bleeding.

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Signs and symptoms for each type of leukemia differ, but common symptoms include:

• Fever or chills
• Persistent fatigue, weakness
• Frequent infections
• Loss of appetite or weight
• Swollen lymph nodes, enlarged liver or spleen
• Easy bleeding or bruising
• Shortness of breath when you're physically active, such as while climbing steps
• Excessive sweating, especially at night
• Bone pain or tenderness

The severity of signs and symptoms depends on the number of abnormal blood cells and where they collect. Early symptoms of leukemia may be overlooked because they may resemble symptoms of the flu and other common illnesses.

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Doctors classify leukemia in two ways. The first is by how fast the leukemia progresses:

• Acute leukemia. In acute leukemia, the abnormal blood cells are immature blood cells (blasts). They can't carry out their normal work, and they multiply rapidly, so the disease worsens quickly. Acute leukemia requires aggressive, immediate treatment.
• Chronic leukemia. This type of leukemia involves more mature blood cells. These blood cells replicate or accumulate more slowly and can function normally for a period of time. Some forms of chronic leukemia produce no symptoms and can go unnoticed or undiagnosed for years.

The second type of classification is by type of white blood cell affected:

• Lymphocytic leukemia. This type of leukemia affects the lymphoid cells or lymphocytes, which form lymphoid or lymphatic tissue. This tissue is the main component of the immune system and is found in places throughout your body, including your lymph nodes, spleen and tonsils.
• Myelogenous (MI-uh-loj-uh-nus) leukemia. This type of leukemia affects the myeloid cells. The myeloid cell line includes cells that later develop into red blood cells, white blood cells and platelet-producing cells.

The major types of leukemia are:

• Acute myelogenous leukemia (AML). This is the most common type of leukemia. It occurs in children and adults. It's also called acute nonlymphocytic leukemia.
• Acute lymphocytic leukemia (ALL). This is the most common type of leukemia in young children. ALL accounts for nearly 75 percent of all childhood leukemias.
• Chronic myelogenous leukemia (CML). This type of leukemia mainly affects adults. It's associated with a chromosome abnormality called the Philadelphia chromosome. A person with CML may have few or no symptoms for months or years before entering a phase in which the leukemia cells grow more quickly.
• Chronic lymphocytic leukemia (CLL). With CLL, another common adult leukemia, you may feel well for years without treatment. CLL is more common in Jewish people of Russian or Eastern European descent. It almost never affects children.

Other, rarer types of leukemia include hairy cell leukemia and chronic myelomonocytic leukemia.

Doctors don't understand the exact cause of leukemia. It seems to develop from a combination of genetic and environmental factors.

Acute leukemia begins with one or a few white blood cells that have a lost or damaged DNA sequence. These cells remain immature in what's known as a blast form, but maintain the ability to multiply. Because they don't mature and then die as normal cells do, they accumulate and begin to interfere with functions of vital organs. Eventually, they overwhelm the production of healthy cells.

Chronic leukemia involves more mature blood cells. They replicate and accumulate more slowly, so the progression of the disease is slower but it can still be deadly. Experts aren't sure why this process begins.

Whatever the reason, having too few normal white blood cells eventually leads to infection, anemia and excessive bleeding. Having too many abnormal white blood cells can impair the function of bone marrow and infiltrate other organs. Death usually results from bleeding or infection.

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These factors place you at an increased risk of developing some types of leukemia:

• Cancer therapy. People who've had certain types of chemotherapy and radiation therapy for other cancers have a slightly greater risk of developing certain types of leukemia many years later.
• Genetics. Genetic abnormalities seem to play a role in the development of leukemia. Certain genetic diseases, such as Down syndrome, are associated with increased risk of leukemia.
• Exposure to radiation and certain chemicals. People exposed to very high levels of radiation, such as survivors of an atomic bomb blast or a nuclear reactor accident, have an increased risk of developing leukemia. Exposure to certain chemicals, such as benzene — which is found in unleaded gasoline, tobacco smoke and the chemical industry — is also linked to greater risk of some kinds of leukemia.
• Smoking. As many as 20% of people with acute myelogenous leukemia (AML) smoke or use other tabacco products.

However, most people with known risk factors don't get leukemia. And many people with leukemia have none of these risk factors.

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Unlike other types of cancer, leukemia isn't a solid tumor that can be surgically removed. The source of the problem is really the bone marrow. But you can't just remove bone marrow, because it produces three basic types of cells — white blood cells, red blood cells and platelets.

Treatment for leukemia is complex. It depends on many factors, including your age and overall health, the type of leukemia you have and whether it has spread to other parts of your body.

Therapies used to fight leukemia include:

• Chemotherapy. Chemotherapy is the major form of treatment for leukemia. This treatment uses chemical agents to kill leukemia cells. Depending on the type of leukemia you have, you may receive a single drug or a combination of one or more drugs. These drugs may come in a pill form, or they may be injected directly into a vein.
• Biological therapy. Also known as immunotherapy, biological therapy uses substances that bolster your immune system's response to cancer.
• Radiation therapy. Radiation therapy uses X-rays or other high-energy rays to damage leukemia cells and stop their growth. You may receive radiation in one specific area of your body where there is a collection of leukemia cells, or you may receive radiation directed at your whole body.
• Bone marrow transplant. This process replaces your leukemic bone marrow with leukemia-free marrow. In this treatment, you receive high doses of chemotherapy or radiation therapy, which destroys your leukemia-producing blood marrow. This marrow is then replaced by bone marrow from a compatible donor. In some cases, you may also be able to use your own bone marrow for transplant (autologous transplant). This is possible if you go into remission and then save healthy bone marrow for a future transplant, in case the leukemia returns.
• Stem cell transplant. Stem cell transplant is similar to bone marrow transplant except the cells are collected from stem cells that circulate in the bloodstream (peripheral blood), after using a medicine that causes cells to be released from the bone marrow. The cells used for transplant can be your own healthy cells (autologous transplant), or they can be collected from a compatible donor (allogeneic transplant). This procedure is used more frequently than bone marrow transplant because of shortened recovery times and possible decreased risk of infection.
• Clinical trials. Some people with leukemia choose to enroll in clinical trials to try out experimental treatments or new combinations of known therapies.
• Supportive care. No matter what kind of cancer therapy you choose, you'll likely need medications to control pain and side effects.

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The overall five-year survival rate for all patients with acute and chronic leukemia is 44%.

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* Text Resources: The Mayo Clinic Staff, Leukemia & Lymphoma Society