Acute myeloid leukemia (AML), also known as acute myelogenous leukemia, is a cancer of the myeloid line of white blood cells, characterized by the rapid proliferation of abnormal cells which accumulate in the bone marrow and interfere with the production of normal blood cells. AML is the most common acute leukemia affecting adults, and its incidence increases with age. While AML is a relatively rare disease overall, accounting for approximately 1.2% of cancer deaths in the United States, its incidence is expected to increase as the population ages.
The symptoms of AML are caused by replacement of normal bone marrow with leukemic cells, resulting in a drop in red blood cells, platelets, and normal white blood cells. These symptoms include fatigue, shortness of breath, easy bruising and bleeding, and increased risk of infection. While a number of risk factors for AML have been elucidated, the specific cause of AML remains unclear. As an acute leukemia, AML progresses rapidly and is typically fatal in weeks to months if left untreated.
Acute myeloid leukemia is a potentially curable disease; however, only a minority of patients are cured with current therapy. AML is treated initially with chemotherapy aimed at inducing a remission; some patients may go on to receive a hematopoietic stem cell transplant.
Areas of active research in acute myeloid leukemia include further elucidation of the cause of AML; identification of better prognostic indicators; development of new methods of detecting residual disease after treatment; and the development of new drugs and targeted therapies.
Signs and symptoms:
Most signs and symptoms of AML are due to an increased number of malignant white blood cells displacing or otherwise interfering with production of normal blood cells in the bone marrow. A lack of normal white blood cell production makes the patient susceptible to infections (while the leukemic cells themselves are derived from white blood cell precursors, they have no infection-fighting capacity). A lack of red blood cells (anemia) can cause fatigue, paleness, and shortness of breath. A lack of platelets can lead to easy bruising or bleeding with minor trauma.
The early signs of AML are often non-specific, and may be similar to those of influenza or other common illnesses. Some generalized symptoms include fever, fatigue, weight loss or loss of appetite, shortness of breath with exertion, anemia, easy bruising or bleeding, petechiae (flat, pin-head sized spots under the skin caused by bleeding), bone pain and joint pain and persistent or frequent infections.
Enlargement of the spleen may occur in AML, but it is typically mild and asymptomatic. Lymph node swelling is rare in AML, in contrast to acute lymphoblastic leukemia. The skin is involved about 10% of the time in the form of leukemia cutis. Rarely, Sweet's syndrome, a paraneoplastic inflammation of the skin, can occur with AML.
Some patients with AML may experience swelling of the gums due to infiltration of leukemic cells into the gum tissue. Rarely, the first sign of leukemia may be the development of a solid leukemic mass or tumor outside of the bone marrow, called a chloroma. Occasionally, a person may show no symptoms, and the leukemia may be discovered incidentally during a routine blood test.
Treatment:
Treatment of AML consists primarily of chemotherapy, and is divided into two phases: induction and postremission (or consolidation) therapy. The goal of induction therapy is to achieve a complete remission by reducing the amount of leukemic cells to an undetectable level; the goal of consolidation therapy is to eliminate any residual undetectable disease and achieve a cure.
Induction:
As of 2006, all FAB subtypes except M3 are usually given induction chemotherapy with cytarabine (ara-C) and an anthracycline (such as daunorubicin or idarubicin). Other alternatives, including high-dose ara-C alone, may also be used. Because of the toxic effects of therapy, including myelosuppression and an increased risk of infection, induction chemotherapy may not offered to the very elderly. Induction chemotherapy usually requires a hospitalization of about 1 month to receive the chemotherapy and recover from its side effects.
Induction chemotherapy is known as "7 and 3" because the cytarabine is given as a continuous IV infusion for seven consecutive days, while the anthracycline is given for three consecutive days as an IV push. Up to 70% of patients will achieve a remission with this protocol.
The M3 subtype of AML, also known as acute promyelocytic leukemia, is almost universally treated with the drug ATRA (all-trans-retinoic acid) in addition to induction chemotherapy.Care must be taken to prevent disseminated intravascular coagulation (DIC), complicating the treatment of APL when the promyelocytes release the contents of their granules into the peripheral circulation. APL is eminently curable with well-documented treatment protocols.
The goal of the induction phase is to reach a complete remission. Complete remission does not mean that the disease has been cured; rather, it signifies that no disease can be detected with available diagnostic methods (i.e., <5% leukemic cells remain in the bone marrow). Complete remission is obtained in about 50%–75% of newly diagnosed adults, although this may vary based on the prognostic factors described above.
The durability of remission depends on the prognostic features of the original leukemia. In general, all remissions will fail without consolidation (post-remission) chemotherapy, and consolidation has become an important component of treatment.
Consolidation:
Even after complete remission is achieved, leukemic cells likely remain in numbers too small to be detected with current diagnostic techniques. If no further postremission or consolidation therapy is given, almost all patients will eventually relapse. Therefore, more therapy is necessary to eliminate non-detectable disease and prevent relapse — that is, to achieve a cure.
The specific type of postremission therapy is individualized based on a patient's prognostic factors and general health. For good-prognosis leukemias , patients will typically undergo an additional 3–5 courses of intensive chemotherapy, known as consolidation chemotherapy.For patients at high risk of relapse (e.g. those with high-risk cytogenetics, underlying MDS, or therapy-related AML), allogeneic stem cell transplantation is usually recommended if the patient is able to tolerate a transplant and has a suitable donor. The best postremission therapy for intermediate-risk AML (normal cytogenetics or cytogenetic changes not falling into good-risk or high-risk groups) is less clear and depends on the specific situation, including the age and overall health of the patient, the patient's personal values, and whether a suitable stem cell donor is available.
Relapsed AML:
Despite aggressive therapy, however, only 20%–30% of patients enjoy long-term disease-free survival. For patients with relapsed AML, the only proven potentially curative therapy is a stem cell transplant, if one has not already been performed. In 2000, Mylotarg (gemtuzumab zogamicin) was approved in the United States for patients aged more than 60 years with relapsed AML who are not candidates for high-dose chemotherapy.
Patients with relapsed AML who are not candidates for stem cell transplantion, or who have relapsed after a stem cell transplant, should be strongly considered for enrollment in a clinical trial, as conventional treatment options are limited. Agents under investigation include cytotoxic drugs such as clofarabine as well as targeted therapies such as farnesyl transferase inhibitors, decitabine, and inhibitors of MDR1 (multidrug-resistance protein). Since treatment options for relapsed AML are so limited, another option which may be offered is palliative care.
For relapsed acute promyelocytic leukemia (APL), arsenic trioxide has been tested in trials and approved by the Food and Drug Administration. Like ATRA, arsenic trioxide does not work with other subtypes of AML.
