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Acute Myeloid Leukemia
By admin at 2006-12-03 07:59

What Is Acute Myeloid Leukemiaterm?

 

Acute myeloid leukemia (AML), also known as acute myelocytic leukemia or acute myelogenous leukemia, is a cancer that begins in cells that normally develop into blood cells. The disease is characterized by the proliferation of immature cells termed "blasts." These blasts eventually overrun the marrow to the detriment of normal cells and the patient dies. When the number of abnormal blasts reaches 20% or greater the term "Leukemia" is used.

 

"Acute" means that the leukemia develops quickly, and if not treated, would probably be fatal in a few months. Often life expectancy is very short as the patient does not realize that their fatigue is the result of a disease and when finally hospitalized are already in "blastterm crisis".

 

Most cases of AML develop from cells that would turn into white blood cells, but some cases of AML develop in other types of blood-forming cells, except in lymphocytes. Acute leukemia that develops in lymphocytes is called acute lymphocytic leukemia AML starts in the bone marrow (the soft inner part of the bones), but in most cases it quickly moves into the blood. It can sometimes spread to other parts of the body including the lymph nodes, liver, spleen, central nervous system (brain and spinal cord), and testes. Other types of cancer can start in these organs and then spread to the bone marrow. But these cancers that start elsewhere and then spread to the bone marrow are not leukemia.

 

Normal Bone Marrow and Lymphoid Tissue

Bone marrow is the soft inner part of some bones such as the skull, shoulder blade, ribs, pelvis, and backbones. The bone marrow is made up of blood-forming stem cells, lymphoid tissue, fat cells, and supporting tissues that aid the growth of blood-forming cells. The blood-forming stem cells continually reproduce to form new cells. Some of these new cells stay stem cells while others go through a series of changes. They stop reproducing and eventually become one of the three main types of blood cells - red blood cell components, white blood cells, or platelets.

 

Red blood cells

Red blood cells contain hemoglobin, which is the substance that gives blood its red color. Hemoglobin allows the red blood cells to carry oxygen from the lungs to all other tissues in the body. Anemia (having too few red blood cells in the body) typically causes weakness, fatigue, and shortness of breath because the tissues are not getting enough oxygen.

Platelets

 

Platelets are actually cell fragments made by a type of bone marrow cell called the megakaryocyte. Platelets are important patching breaks in the blood vessels. A shortage of platelets is called thrombocytopenia. A person with thrombocytopenia will bleed and bruise easily.

 

White blood cells

 

White blood cells are important in defending the body against infections. Lymphocytes are one type of white blood cell. The other white blood cells are monocytes, neutrophils, basophils, and eosinophils. Lymphocytes are the main cells that make up lymphoid tissue, a major part of the immune system. Lymphoid tissue is found in lymph nodes, the thymus, the spleen, the tonsils and adenoids, and the bone marrow and is scattered throughout the digestive and respiratory systems and the bone marrow. The 2 types of lymphocytes are known as B lymphocytes (B cells) and T lymphocytes (T cells).

* B lymphocytes protect the body from invading germs by changing (maturing) into plasma cells, which produce antibodies. These antibodies attach to the germs, such as bacteria, viruses, and fungi. Once the germ has been coated in this way, granulocytes can recognize and destroy it. * T lymphocytes can recognize cells infected by viruses and destroy these cells directly. Monocytes, which are related to the granulocyte group, also are important in protecting the body against bacteria. They start in the bone marrow as blood-forming monoblasts and develop into mature monocytes. After circulating in the bloodstream for about a day, monocytes enter tissues to become macrophages, which can destroy some germs by surrounding and digesting them. Macrophages are also important in helping lymphocytes to recognize germs and begin producing antibodies to fight them. Neutrophils, basophils, and eosinophils are types of granulocytes - white blood cells that have granules in them, which are spots that can be seen under the microscope. These granules contain enzymes and other substances that can destroy germs that cause infections. The 3 types of granulocytes are distinguished by the size and color of their granules. Granulocytes develop from blood-forming cells called myeloblasts to become mature, infection-fighting cells. These white blood cells mainly function to destroy invading bacteria. Any of the blood-forming or lymphoid cells from the bone marrow can turn into a leukemia cell. Once this change takes place, the leukemia cells fail to go through their normal process of maturing. Although most people think that in leukemia the cells reproduce too quickly, in most cases the problem is that they don’t die. This means that as they survive, they accumulate. Eventually, these cells spill out into the bloodstream and spread to other organs, where they can prevent other cells in the body from functioning normally.

 

Types of Leukemia

Not all leukemias are the same. Leukemias are divided into 4 main types with several subtypes in order to better predict each patient's prognosis and help doctors select the best treatment for each patient. Today we are able to characterize the prognosis of subtypes of Leukemia based on the patients cytogenetic profile.

Acute leukemia versus chronic leukemia: The first factor to consider in classifying a patient's leukemia is whether most of the abnormal cells are mature (resemble normal circulating white blood cells) or immature. In acute leukemia, the bone marrow cells are unable to properly mature. Immature leukemic cells, which are often called blasts, continue to reproduce and accumulate. Without treatment, most patients with acute leukemia would live less than a few months. Some subtypes of acute leukemia respond well to treatment and many patients are cured, while other types of acute leukemia have a less favorable outlook. In chronic leukemia the cells can mature partly but not completely. They are not really normal. They generally do not fight infection as well as do normal white blood cells. And, of course, they survive longer, build up, and crowd out normal cells. Myeloid leukemia versus lymphocytic leukemia: The second factor to consider in classifying leukemia is the type of bone marrow cells that are affected. If granulocytes or monocytes are involved, the leukemia is classified as myeloid leukemia (also known as myelogenous or myelocytic leukemia). If the cancer develops from bone marrow lymphocytes, it is called lymphocytic (or lymphoblastic) leukemia. (Malignant lymphomas are also cancers of lymphocytes. But, unlike lymphocytic leukemias which develop in the bone marrow, lymphomas develop from lymphocytes in lymph nodes or other organs.)

 

Four main types of leukemia: By considering whether they are acute or chronic, and whether they are myeloid or lymphocytic, leukemias can be divided into 1 of 4 main types:

* acute myeloid leukemia (AML)

* chronic myeloid leukemia (CML) or chronic myelogenous leukemia

* acute lymphocytic leukemia (ALL) or acute lymphoblastic leukemia

* chronic lymphocytic leukemia (CLL)

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