Science Fair Project Encyclopedia
Acute myelogenous leukemia
Acute myelogenous leukemia (AML), also known as acute myeloid leukemia, is a cancer of the myeloid line of white blood cells. It is the most commonly diagnosed type of adult leukemia, and is rare among children.
These malignant cells called myeloblasts fail to mature into the different types of blood cells, a process called differentiation. If differentiation does not occur, the myeloblasts accumulate and overtake the number of healthy blood cells, spreading into the bloodstream and other vital organs. The lack of healthy blood cells results in symptoms such as anaemia and abnormal bruising.
Myeloid leukemias are characterized as "acute" or "chronic" based on how quickly they progress if not treated. Chronic myelogenous leukemia (CML) is often without symptoms and can remain dormant for years before transforming into a blast crisis, which is markedly similar to AML.
Acute myelogenous leukemia have been divided into 8 subtypes, M0 through to M7 under the French-American-British (FAB) classification system based on the type of cell from which the leukemia developed and degree of maturity. This is done by examining the appearance of the malignant cells under light microscopy or cytogenetically by characterization of the underlying chromosomal abnormality. Each subtype is characterised by a particular pattern of chromosomal translocations and have varying prognoses and responses to therapy.
The eight different subtypes are:
- M0 (undifferentiated AML)
- M1 (myeloblastic, immature)
- M2 (myeloblastic, mature)
- M3 (promyelocytic), or acute promyelocytic leukemia (APL)
- M4 (myelomonocytic)
- M5 (monocytic)
- M6 (erythroid)
- M7 (megakaryoblastic)
Subtype M2 is the most common among AML patients and comprises approximately 25% of adult AML patients, it also carries a favourable prognosis. Subtype M3 carries the best prognosis, whilst M0, M6, and M7 carry the worst prognoses.
Most signs and symptoms of AML are due to the increased numbers of malignant white blood cells and a lack of normal blood cell production in the bone marrow. The early signs of AML may be similar to those of influenza or other common illnesses, and often have many different signs and symptoms. Some generalized symptoms include:
- Weight loss or loss of appetite
- Shortness of breath (Dyspnea)
- Easy bruising or bleeding
- Petechiae - flat, pin-head sized spots under the skin caused by bleeding
- Bone and joint pain
- Persistent infections
Some patients of AML with subtype M5 may experience swelling of the gums due to the spread of the disease there. Occasionally, a person may show no symptoms and the leukemia is discovered during a routine blood test. Usually, the symptoms of AML appear within a few weeks and experience sudden onset of illness.
Diagnosing AML usually begins with a physical exam at a doctor's office. An abnormal blood test reading will then result in further testing in a hospital with a hematologist to determine AML. Most patients with AML will experience a high count of malignant white blood cells, and low counts of red blood cells and platelets.
A bone marrow aspiration or biopsy is then conducted to identify the type of abnormal blood cells and determine the best treatment plan for the patient. The marrow is taken from the back of the hipbone or occasionally it may be taken from the sternum.
There is ongoing research into the causes of Acute Myelogenous Leukaemia however it is not known for sure what causes it.
It is thought that in very rare cases, excessive exposure to harmful chemicals such as benzene and radiation such as atomic bomb explosions may trigger abnormal DNA mutations, resulting in leukemia. Patients who have received previous treatment with certain drugs (alkylating agents) are also at higher risk of developing AML.
Because of inherited genetic defects, some individuals are born with an abnormal immune system, which causes them to be at higher risk of developing leukemia.
Chemotherapeutic treatment is divided into two phases: induction and postremission therapy. In all FAB subtypes except M3, the usual treatment includes cytarabine (Ara-C) and an anthracycline (such as daunorubicin or idarubicin).
Complete remission is obtained in about 70 percent of newly diagnosed adults. The bone marrow is examined for malignant cells after each course of treatment. Remission can be achieved after one to three courses.
Postremission therapy can include more intensive chemotherapy or bone marrow transplant.
The M3 subtype, also known as APL, is almost universally treated by the drug ATRA (all-trans-retinoic acid). For relapsed APL, where ATRA doesn't always work, arsenic trioxide has been tested in trials and approved by the FDA. Like ATRA, arsenic trioxide does not work with other sub-types.
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