Acute Myelogenous Leukemia (AML)
Acute myelogenous leukemia occurs when a genetic defect arises in the one of the cells in the myeloid stem cell line, one of the two blood cell lines found in the bone marrow. The problem can arise in any of several types of early cells in this line. The type of cell it arises in determines how the disease is classified into a subtype and may guide treatment decisions. AML is also sometimes called acute nonlymphocytic leukemia, or ANLL.
When the genetic defect occurs, the affected cell fails to mature properly and multiples continuously. The resulting abnormal cells, called leukemic blasts, do not function properly. They also build up in the bone marrow, crowding out other types of blood cells. The result is a shortage of red blood cells, platelets, and healthy white blood cells. These shortages cause anemia, bleeding and bruising, and a diminished ability to fight off infections.
Symptoms
Many people who develop AML feel fatigued, achy, or just "not well." They may feel short of breath and may notice unusual bruising or bleeding, joint or bone pain, or tiny red marks under the skin. They also commonly develop infections. Most of these symptoms are caused by a lack of healthy blood cells of all types.
In some cases, leukemic cells collect in the central nervous system, causing headaches and vomiting. They can also collect in the lymphatic system, causing enlarged lymph nodes. Cells may invade the spleen and liver, leading to swelling and tenderness. The gums may swell and bleed. The leukemic cells may gather in groups under the skin, forming clumps called chloromas or granulocytic sarcomas.
Most people have symptoms for fewer than three months before leukemia is diagnosed. Sometimes the onset of symptoms is so dramatic that diagnosis is sought after only a few days.
Who Gets AML
Acute myelogenous leukemia is the most common type of leukemia found in adults. The average age of patients is 65.
Children can develop AML as well; it accounts for about 800 cases of children's leukemia each year.
Risk Factors
It is rarely possible to say exactly what caused one person's leukemia. Scientists do know, however, that some risk factors exist for AML.
Smoking is one risk factor; chemicals in tobacco smoke can enter the bloodstream and affect the body beyond the lungs. About 20 percent of all cases of AML are believed to be caused by smoking. Other risk factors include very high doses of radiation and various chemicals.
People who were treated for other cancers, such as lymphoma, childhood ALL, or breast or ovarian cancer, with certain chemotherapy drugs are also at risk of developing AML. These drugs include mechlorethamine, procarbazine, chlorambucil, etoposide, teniposide, and cyclophosphamide. The genetic disorders known as Down syndrome and Fanconi anemia also put a person at higher than average risk for AML.
Risk factors, however, account for only a small percentage cases of AML. Most people who develop the disease have no risk factors. Other than not smoking, there is little that anyone can do to avoid AML.
Subtypes of AML
The classification scheme for AML divides the disease into several different subtypes. These subtypes are identified by looking at blood cells under a microscope and by doing other laboratory tests. Knowing which subtype is present can sometimes help in predicting the course of the disease and in selecting the most effective therapy.
The subtypes are based on which line of blood-forming cells is involved and the maturity of the affected cells. Each reflects a point at which the normal maturation process was halted and immature cells started to proliferate.
- M0: Undifferentiated AML. This subtype is found in 5 percent of AML cases.
- M1: Myeloblastic leukemia, with few or no mature cells. This subtype occurs in the cell line that matures into the white blood cells known as neutrophils. Few if any cells are differentiating into their later forms. This form occurs in 15 percent of cases.
- M2: Myeloblastic leukemia with maturation. Like M1, this subtype occurs in the cell line that matures into neutrophils, but it arises a bit further along the maturation scale. Many blasts are present, as in the case of M1, but some cells are maturing. It occurs in about 25 percent of cases.
- M3: Promyelocytic leukemia. Like M1 and M2, this subtype occurs in the cell line that matures into neutrophils, but even further along the maturation scale. It accounts for about 10 percent of cases. It is also called acute promyelocytic leukemia.
- M4: Myelomonocytic leukemia. Here, maturation is arrested fairly early in the cell line that produces both monocytes and neutrophils. It is found in about 25 percent of all cases.
- M4 eos: Myelomonocytic leukemia with eosinophilia. This type is very rare.
- M5: Monocytic leukemia. This form of AML arises fairly late in the cell line that produces monocytes. It accounts for about 10 percent of all cases.
- M6: Erythroid leukemia or erythroleukemia. This subtype is diagnosed when early cells in the line that produces red blood cells are damaged. Immature red and white blood cells may be seen in the blood. It occurs in only 5 percent of AML cases.
- M7: Megakaryocytic or megakaryoblastic leukemia. This form arises in the cell line that produces platelets. It accounts for 5 percent of cases.
Prognostic Factors
Some subtypes of AML have been found to have a more favorable response to treatment than others. People who have the M3 or M4 eos subtype often have the best response to treatment. Patients with the M2 subtype and a translocation between chromosomes 8 and 4 also have a better response to therapy. Those who have the M5 or M6 subtype often have a less favorable response. In addition, patients who are 60 or older, have certain chromosomal abnormalities, have an initial leukocyte count of 100,000 or higher, or who have been treated before with radiation or chemotherapy tend to have a poorer outcome.
Note that these prognostic factors were developed by looking at large groups of patients; they do not necessarily predict the outcome for any single patient.
