advertisement
|
advertisement |
 |
||||
 |
|
|||
|
||||
|
Acute Lymphocytic Leukemia Overview Acute lymphocytic leukemia (ALL) is one of the four main types of leukemia. Like all cancers, leukemia is characterized by uncontrolled production of abnormal cells. In ALL, the cancer starts in the precursor cells of lymphocytes—a type of white blood cell produced in the bone marrow. This disease is considered acute because ALL spreads rapidly. In most cases, the cancer cells quickly leave the bone marrow and invade the blood. The course of the disease varies among the different subtypes of ALL. However, if left untreated, acute lymphocytic leukemia is eventually fatal; it will spread to the lymph nodes, spleen, liver, central nervous system, and other organs. Also known as acute childhood leukemia, ALL is the most common cancer in children. Of the estimated 5,200 people expected to be diagnosed this year, 3 out of 5 will be children or adolescents 19 years of age or younger. The most common age at diagnosis is 13. The likelihood of developing the disease decreases dramatically with age starting at about 20 years of age. Afro-Americans are less likely to develop ALL than other ethnicities. Acute lymphocytic leukemia is a serious health concern and requires timely, aggressive treatment. The treatment depends on the subtype of ALL, how far it has progressed, white blood cell count at diagnosis, and one's age and overall health. Thankfully, most patients respond well to treatment, especially children. Most children who develop ALL are cured before the age of 15 years. In adults, a relapse of ALL is not uncommon. This year approximately 1,400 people are expected to die from acute lymphocytic leukemia. As treatment therapies continue to evolve, an increasing number of adults and children with leukemia can look forward to surviving their disease and enjoying a better quality of life. This section contains more on: Need-to-Know-Anatomy Blood is made up of cells suspended in plasma. Plasma is a watery liquid that contains proteins, hormones, minerals, vitamins, and antibodies. Blood cells are produced in the bone marrow. The bone marrow is the soft spongy center of the larger bones in the body. It contains blood-forming cells and fat cells in a fibrous jungle of tissue that nurtures the growth of blood cells. As blood flows through the bone marrow, the mature blood cells are released into the bloodstream to circulate throughout the body. Blood circulating outside of the bone marrow in the vessels and organs of the body is known as peripheral blood. In the bone marrow, blood cells are constantly dividing and maturing to replace old cells. The production of blood cells begins with hematopoietic (blood-forming) stem cells. Although they are commonly referred to as "stem cells," these cells are not the same as embryonic stem cells that are used in medical research. Most cells in the body are able to duplicate themselves to reproduce only a single type of cell, while stem cells can develop into many different kinds of cells. Hematopoietic stem cells are capable of developing into any of the three types of blood cells as needed by the body: red blood cells, platelets, and white blood cells. Red blood cells or erythrocytes account for about 35 to 50 percent of the cells in blood. Red blood cells are filled with hemoglobin, which enables them to deliver oxygen to the tissues of the body. When blood circulates through the lungs, the hemoglobin releases carbon dioxide and picks up oxygen. The oxygen-rich cells then circulate in the body where they deliver oxygen to tissues in exchange for carbon dioxide before cycling back to the lungs. If the red blood cell count falls below 35 percent, the cells can no longer meet the body's demand for oxygen and anemia can develop. Anemia, which can be associated with some forms of leukemia, can lead to shortness of breath, fatigue, or pale skin. Platelets, also known as thrombocytes, are fragments of cells that help control blood loss. Platelets adhere to torn surfaces to repair damaged vessels and clump together or clot to stop bleeding. In a healthy body, the platelet count is between 150,000 and 450,000 platelets per microliter, the exact range varies slightly between laboratories. If the platelet count drops below this level, a person may bruise more easily, bleed longer, and have nosebleeds or bleeding gums. If the platelet count drops below 20,000 platelets per microliter, spontaneous bleeding may develop. White blood cells or leukocytes are the warriors of the immune system. Unlike red blood cells or platelets, white blood cells are able to enter the tissues of the body in order to fight infections caused by fungi, bacteria, or viruses. Changes in the white blood cell count can indicate infection, development of leukemia or other conditions. Neutrophils, eosinophils, basophils, monocytes, and lymphocytes are the main types of white blood cells. Lymphocytes are the building blocks of the immune system and are found throughout the body in the lymph nodes, spleen, tonsils and adenoids, the digestive and respiratory systems, thymus, and the bone marrow. They travel in their own circulatory system known as the lymphatic system and the blood stream. Lymphocytes can be divided into two main types; B cells and T cells, the latter of which include many subtypes. Different types of acute lymphocytic leukemia are classified based on the subtypes of lymphocytes affected. White blood cell counts in a healthly individual typically range from 4,500 to about 10,000 cells per microliter; this range may vary slightly depending upon the laboratory performing the analysis. Blood cells pass through several stages of development. Starting as a hematopoietic stem cell, the blood cell first differentiates into either a myeloid stem cell or lymphoid stem cell. These cells develop into what are known as blasts or immature blood cells. Myeloid blasts ultimately differentiate into red blood cells, platelets, neutrophils, eosinophils, basophils, or monocytes. Lymphoid blasts ultimately mature into lymphocytes. In a healthy body, the life span of a blood cell ranges from a period of hours to months depending upon cell type. The rate at which cells are produced in the bone marrow is regulated much like heat in a house. As the temperature drops in a house, the thermostat calls for heat. When the temperature reaches the thermostat's set point, the thermostat turns off the furnace. In the body, there are many different triggers for the bone marrow to produce blood cells. For example, an infection is a common trigger for the production of white blood cells. Once the infection is under control, the rate of white blood cell production drops off until it returns to normal. Causes For people with acute lymphocytic leukemia, the production of lymphocytes in their bone marrow has gone awry. The lymphoid blasts (immature blood cells) are not developing into normal-functioning lymphocytes with a finite life span. Instead, the lymphoid blasts remain immature and persist indefinitely because of a mutation in the DNA of the lymphoid stem cell. DNA can be thought of as the set of instructions for cell reproduction and growth. In humans, the DNA is organized into 23 pairs of chromosomes. A mutation in the DNA means the set of instructions for cell development has become jumbled. Instead of maturing into normal blood cells, the cells develop into cancerous leukemia cells. Doctors can check for some mutations associated with leukemia by looking for changes in the size and/or shape of a chromosome. Researchers and doctors don't yet understand exactly what causes these mutations associated with ALL. The mutations associated with leukemia are typically not inherited, but the tendency to develop the mutation may be inherited. Some people with ALL have the mutation known as the Philadelphia chromosome. Originally associated with acute myeloid leukemia, the Philadelphia chromosome is present in about one quarter of the people with ALL as well. With this mutation, parts of chromosome numbers 9 and 12 swap places with each other. In ALL, the mutation in the DNA affects the development of the lymphoid cells in three critical ways. First, the cell is prevented from developing beyond the primitive blast stage. These abnormal lymphoid blasts are unable to carry out their immune system functions. The mutation also affects the life span of the cell. Leukemia cells persist beyond the life span of normal cells; they simply do not die off in an orderly manner. Finally, the bone marrow continues to produce leukemia cells incessantly, like heat production in a house with a broken thermostat. This set of circumstances results in the proliferation of lymphoid blasts in the blood. The accumulation of lymphoid blasts in the blood causes two fundamental problems. The immune system is compromised because the defective lymphocytes are not able to fight infection. Over time a second problem arises because of the proliferation of leukemia cells. The leukemia cells crowd out the normal blood cells and platelets; this interferes with delivery of oxygen and blood clotting, and worsens an already compromised immune system. Risk Factors Medical researchers are just beginning to identify the complex interplay of factors that may lead to the development of leukemia. Leukemia is caused by spontaneous mutations in the DNA of blood cells. Although leukemia is not considered an inherited disease, some people inherit a predisposition for developing the genetic mutations that cause leukemia. However, not everyone with the mutation develops leukemia. The exact trigger for the mutation and subsequent development of leukemia is unknown. However, some factors have been linked to the development of the acute lymphocytic leukemia. The risk factors for leukemia fall into three categories: those you can control through lifestyle choices, those traits you are born with, and those associated with environmental exposures. Most people who have a risk factor for leukemia do not develop leukemia; and most people who develop the disease do not have a risk factor. However, understanding your risk allows you to balance the value you place on your health with the risk that an activity may compromise your health in the future. Possible risk factors for acute lymphocytic leukemia: • Being male—slight increase in risk • Being Caucasian—slight increase in risk • Exposure to very high levels of radiation such as an atomic bomb or nuclear accident. • Having a certain genetic disorder such as Down syndrome or human T-cell lymphoma leukemia virus (HTLV-1) • Having a sibling with leukemia • Having had certain types of chemotherapy including alkylating agents or topoisomerase inhibitors. Most of these diagnoses occur within nine years of treatment of Hodgkin's disease, non-Hodgkin's lymphoma, or childhood acute lymphocytic leukemia. Types of Acute Lymphocytic Leukemia Different types of acute lymphocytic leukemia can be distinguished based on the cell's phenotype or physical characteristics. Flow cytometry, cytogenetic testing, and molecular studies are tests used to classify or immunophenotype leukemia cells. For people with ALL, the immunophenotype refers to whether the leukemia begins in the "B" lymphocytes or the "T" lymphocytes. Approximately 85 percent of ALL are B cell, which can be further classified into three types: early pre-B cell, pre-B cell, and mature B lymphocyte cell. Subtypes involving the T lymphocyte are classified as either pre-T cell or mature T cell. Identifying subtype of ALL helps doctors predict which treatment will be most effective and is also used as an indicator of the survival outlook for the patient. Mature B cell and T cell ALL are the most difficult to cure while patients with early pre-B cell or pre-B cell tend to have the best outcomes for survival. Identifying subtype of ALL helps doctors predict which treatment will be most effective and is also used as an indicator of the survival outlook for the patient. Mature B cell and T cell ALL are the most difficult to cure while patients with early pre-B cell or pre-B cell tend to have the best outcomes for survival. Links More information on acute lymphocytic leukemia is available at these websites recommended by the U.S.News & World Report library:
Acute Lymphocytic Leukemia
Acute Lymphocytic Leukemia Clinical Trials
American Cancer Society
National Cancer Institute
The Leukemia and Lymphoma Society
ClinicalTrials.gov
|
Use of this Web site constitutes acceptance of our Terms and Conditions of Use and Privacy Policy.
