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Acute myeloid leukemia
Acute myeloid leukemia (AML) is a group of neoplasms arising from precursor cells committed to the myeloid cell-line differentiation. All of them are characterized by clonal expansion of myeloid blasts. AML manifests by fever, pallor, anemia, hemorrhages and recurrent infections.
Annual incidence rate of AML is estimated to be 1/33,000-1/25,000 in Europe.
Although, AML can occur at any age, it is typically a disease affecting elder people, usually more than 65 years. The main clinical picture consists of a short time period with pallor, fatigue, fever, infections and hemorrhages. Presence of all these features is not compulsory. Central nervous system infiltration is uncommon and mainly related with monocytic variants. Extramedullary accumulation of myeloid blasts in different tissues, mainly skin, can be observed and is known as myeloid sarcoma (see this term). Testes are usually not affected.
Pathogenesis of AML is still unclear but a two-hit model has been suggested as the probable mechanism for leukemogenesis. That means that AML could be the consequence of at least 2 different types of gene mutations. Class I mutations resulting in proliferative advantage while the class II mutations alter the normal hematopoietic differentiation. Examples of class I mutations are those of FLT3-ITD or KIT mutations. Class II mutations include CEBPA mutations. Controversy is also still in the type of cell from which AML arises. While data supporting progenitor cells committed to specific myeloid cell type has been reported, other studies argue in favor for a more immature stem.
Diagnosis relies on laboratory findings showing anemia, thrombocytopenia and leucopenia or leukocytosis which result from disturbed hematopoietic function due to bone marrow and peripheral blood infiltration by immature blast cells. Diagnosis of AML also relies on bone marrow aspirate or biopsy after the disease has been suspected. Bone marrow should have at least 20% of myeloid blasts to be considered as AML. After morphological examination, immunophenotyping of leukemic cells, cytogenetic and molecular analysis should be performed.
Differential diagnosis includes megaloblastic anaemia, myelodysplastic syndromes, acute lymphoblastic leukemia, acute biphenotypic leukemia, chronic myeloid leukemia (myeloid blast phase), and metastases of tumors such rhabdomyosarcoma and neuroblastoma (see these terms).
Management and treatment
For young patients, treatment consists of an induction cycle with cytarabine plus idarubicin or daunorubicin in a typical 3 + 7 schedule with the first objective to reach complete response (CR). About 75% of the patients achieve CR, but virtually all of them will relapse if additional treatment (consolidation therapy) is not given. Based on stratification, patients can be treated with chemotherapy consolidation or allogenic hematopoietic stem cell transplantation (HSCT). Refractory or relapsed AML is treated with a second induction course adding new drugs (such gemtuzumab ozogamicin) to the standard treatment. Some drugs such as azacitidine or decitabine are available for the treatment of elderly AML patients under specific circumstances.
Prognosis varies widely according to cytogenetics, molecular findings, response to induction treatment and age, between others. Overall, long-term survivors account for 40% of young patients. For children less than 15 years, overall survival rates are 60-70%. Prognosis of elder patients is rather poor.