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About Acute Myeloid Leukemia (AML)
Acute myeloid leukemia (AML) is one of two major types of myeloid leukemia. AML is also called acute myelogenous leukemia, acute myeloblastic leukemia, acute granulocytic leukemia or acute nonlymphocytic leukemia. It is the second most common type of leukemia in adults.
In AML, the myeloid stem cells usually develop into a type of immature white blood cell called myeloblasts (or myeloid blasts). The myeloblasts in AML are abnormal and do not become healthy white blood cells. These abnormal blasts are leukemic cells. Sometimes in AML, too many stem cells develop into abnormal red blood cells or platelets. These abnormal red blood cells or platelets are also called leukemia cells or blasts. The leukemia cells can build up in the blood and bone marrow so there is less room for healthy white blood cells, red blood cells and platelets. When this happens, infection, anemia or easy bleeding may occur.
The leukemia cells can spread outside the blood to other parts of the body, including the central nervous system (brain and spinal cord), skin (known as leukemia cutis) and gums. Sometimes leukemia cells form a solid tumor called a granulocytic sarcoma or chloroma (so-called because of its blue-green color). While these tumors may occur almost anywhere, the most common sites are the skin and gums.
AML is an aggressive disease, and commensurately aggressive treatment is required. This may include combination chemotherapy, radiation and/or bone marrow or stem cell transplantation.
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Subtypes of Acute Myeloid Leukemia
There are subtypes of acute myeloid leukemia (AML) based on the type of blood cell that is affected as well as specific genetic characteristics. Genetic mutations called translocations, in which a section of genes on one chromosome is literally swapped with a section of genes on a completely different chromosome, are quite prevalent in AML.
- Acute promyelocytic leukemia (APL), also called acute progranulocytic leukemia, results from the overaccumulation of immature myelocytes called progranulocytes. As with other forms of AML, a genetic translocation is thought to be the cause, with a section of chromosome containing a gene called RARA being translocated in this case. The RARA gene encodes for a receptor for retinoic acid, a derivative of vitamin A. This knowledge has led to APL being treated with all-trans-retinoic acid, to which it is uniquely sensitive and highly therapeutically responsive.
- Juvenile myelomonocytic leukemia (JMML) is a rare childhood cancer that occurs more often in children younger than two years. In JMML, too many bone marrow stem cells develop into two types of white blood cells called myelocytes and monocytes. Some of these bone marrow stem cells never become mature white blood cells. These immature cells, called blasts, are unable to do their usual work. Over time, the myelocytes, monocytes, and blasts crowd out the red blood cells and platelets in the bone marrow. When this happens, infection, anemia or easy bleeding may occur.
- Transient myeloproliferative disorder (TMD) is a disorder of the bone marrow that can develop in newborns who have Down's syndrome. This disorder usually goes away on its own within the first three weeks of life. Infants who have Down's syndrome and TMD have an increased chance of developing AML before three years of age.
- In myelodysplastic syndromes, the bone marrow makes too few red blood cells, white blood cells and platelets. These blood cells may not mature and enter the blood. The treatment for myelodysplastic syndromes depends on how much lower than normal the number of red blood cells, white blood cells or platelets is. Myelodysplastic syndromes may progress to AML.
- Children with Down's syndrome and certain other genetic abnormalities such as neurofibromatosis type 1 have a much greater chance of developing AML, JMML, TMD and myelodysplastic syndrome. Most AML in Down's syndrome patients originates as some type of myelodysplasia. AML patients with Down's syndrome have two important characteristics: 1) they are significantly more responsive to chemotherapy than non-Down AML patients, and 2) their leukemic cells exhibit much greater sensitivity to a chemotherapy drug called cytosine arabinoside.
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Risk Factors
The risk factors for developing childhood AML, childhood chronic myelogenous leukemia, JMML, TMD, and myelodysplastic syndrome are similar. Possible risk factors include:
- Having a brother or sister, especially a twin, with leukemia. Because these disorders often involve chromosome translocations, the same mutation may occur in genetically identical or similar individuals
- Hispanic descent
- Exposure to cigarette smoke or alcohol before birth. Cigarettes are known to contain benzene and other potent leukemogens
- History of myelodysplastic syndrome (also called preleukemia) or aplastic anemia
- Previous chemotherapy or radiation therapy
- Exposure to ionizing radiation or chemicals such as benzene
- Certain genetic disorders such as Down's syndrome, Fanconi anemia, neurofibromatosis type 1 or the congenital genetic condition Noonan's syndrome
Possible risk factors for adult acute myeloid leukemia include the following:
- Male gender
- Smoking, especially after age 60
- Previous chemotherapy or radiation therapy
- Previous treatment for childhood acute lymphoblastic leukemia (ALL). This treatment is likely to have included alkylating agents, which are themselves leukemogenic, and may thus cause secondary malignancies
- Exposure to atomic bomb radiation or the chemical benzene
- History of a blood disorder such as myelodysplastic syndrome
People who think they may be at risk should discuss this with their doctor.
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Symptoms
Possible signs of AML, CML, JMML or myelodysplastic syndromes include fever, feeling tired, and easy bleeding or bruising. Other conditions may cause the same symptoms. Symptoms include:
- Fever with or without an infection
- Night sweats
- Shortness of breath
- Weakness or feeling tired
- Easy bruising or bleeding
- Petechiae (flat, pinpoint spots under the skin caused by bleeding)
- Pain in the bones or joints
- Pain or feeling of fullness below the ribs
- Painless lumps in the neck, underarm, stomach, groin or other parts of the body. Lumps or lesions on the skin, called leukemia cutis (see description above), may be red, blue or purple
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