Acute myeloid leukaemia is a malignant neoplastic disease affecting white blood cells. Acute myeloid leukaemia (AML) is also called acute myelogenous or myelocytic leukaemia.
AML is responsible for about 25% of childhood leukaemias, often developing in infancy. However, the incidence of AML increases with age. It is the most common acute leukaemia in adults, with a median age of onset of 68 years.1
AML arises from the uncontrolled growth of the myeloid cell line in the bone marrow (Figure 1).
This uncontrolled growth leads to a proliferation of immature, non-functional white blood cells, known as “blasts”. These blasts disrupt normal haematopoiesis, which is the formation of blood cell components.
When normal haematopoiesis is impaired this can cause pancytopenia, where there is a reduction in the number of red and white blood cells, as well as platelets.
Low red blood cells (RBC) leads to symptoms and signs of anaemia. Low platelets (thrombocytopaenia) manifest as bleeding and bruising. Low white cells (WCC) lead to an increased susceptibility to infection.
Immature blast cells may enter the bloodstream and infiltrate other organs such as the central nervous system, liver, and skin.
The most common risk factor for AML is myelodysplastic syndrome and other pre-existing haematological disorders.
However, in the majority of cases, AML appears as a de novo malignancy in previously healthy individuals.
The following risk factors are associated with AML:1,3
Thrombocytopaenia: mucosal bleeding, easy bruising, petechiae/purpura, epistaxis, bleeding gums, and heavy menstrual bleeding. Occasionally, patients can present with spontaneous haemorrhage, including intracranial or intra-abdominal haematomas.
Neutropaenia: increased susceptibility to infections. Patients may present with fevers in the presence of a severe and/or recurrent infection. Patients often have a history of upper respiratory infection symptoms that have not improved despite treatment with antibiotics.
Leukaemic infiltration: abdominal discomfort/fullness may be present due to hepatosplenomegaly.
Other important areas to cover in history include:
Past medical history: pre-existing haematological disorders, autoimmune disorders, medication history
The clinical presentation of AML can vary greatly.
Typical clinical findings in AML may include:
Physical signs of anaemia, including pallor and a cardiac flow murmur
Fever and other signs of infection such as lung findings consistent with pneumonia
Thrombocytopaenia can cause petechia, dermal bleeding and ecchymoses
Leukaemic infiltration of the organs can result in hepatosplenomegaly, lymphadenopathy, and swollen gums
Less common findings, which usually appear in later stages, include:
Leukaemia cutis refers to the infiltration of the skin with leukaemia cells
Respiratory distress and altered mental status are clinical signs that may indicate leukostasis. This is a medical emergency, which is characterised by an extremely elevated blast cell count.
Pancytopenia can be caused by a variety of diseases with a wide range of severities. It is important to distinguish a patient with AML from a patient with another haematological disorder.
Table 1. The differential diagnoses of leukaemia.
Paroxysmal nocturnal haemoglobinuria
Systemic lupus erythematous
Drug-induced (e.g. methotrexate)
The diagnostic workup of AML involves the integration of history, clinical presentation, and laboratory results.
A diagnosis of AML is made by either identifying ≥20% myeloid blasts in the bone marrow (or peripheral blood) or detecting specific cytogenetic abnormalities.
Relevant laboratory investigations include:
Full blood count: white cell count may be normal, elevated, or low. Red blood cells may be low, revealing anaemia which is usually normocytic/normochromic. The platelet count may be low (thrombocytopaenia).
Peripheral blood smear: may show myeloblasts which are immature cells with large nuclei, usually with prominent nucleoli. Auer rods may also be seen (Figure 2). These are pathognomonic of myeloblasts and they vary in frequency depending upon the AML subtype. They can be identified as pink/red rod-like granular structures in the cytoplasm. These are myeloperoxidase positive.
Lactate dehydrogenase (LDH): may be elevated due to increased cell turnover
Uric acid: may be elevated due to increased cell turnover
Coagulation profile: may be deranged or show disseminated intravascular coagulation
Bone marrow biopsy
A bone marrow biopsy is required to stage the disease. The percentage of blasts determines chronic vs accelerated vs blast crisis.
Typically, both bone marrow aspiration and bone marrow trephine biopsy are performed. An aspirate is when a syringe of liquid bone marrow is filled while a trephine is when a 1-2cm piece of core bone marrow is removed in one piece.
In AML, the bone marrow is usually hypercellular because the normal cellular components are partially or totally replaced by immature or undifferentiated cells.
Analysis that is typically performed on the bone marrow includes:
Immunophenotyping by flow cytometry
Cytogenetics: a study of chromosomal structure, location, and function in cells
Fluorescence in situ hybridisation (FISH): a laboratory technique for detecting and locating a specific DNA sequence on a chromosome
Molecular analyses: molecular genetic techniques involve a combination of procedures to isolate and analyse the DNA or RNA transcribed from a particular gene
Flow cytometry may be performed with peripheral blood or marrow aspirate.
It is used to identify circulating myeloblasts by characteristic patterns of surface antigen expression. The patterns of surface antigen expression vary amongst AML subtypes, but the majority express CD34, HLA-DR, CD117, CD13, and CD33.4,5,6,7
AML is classified using either the World Health Organization (WHO) classification or the French-American- British (FAB) classification.
World Health Organization (WHO) 2016 classification
The World Health Organization (WHO) classification system is based upon a combination of morphological, immunophenotypical, genetic, and clinical features:9,10
AML with recurrent genetic abnormalities
AML with myelodysplasia (MDS)-related changes
Therapy-related myeloid neoplasms
AML, not otherwise specified
Myeloid proliferations related to Down’s syndrome
French-American-British (FAB) classification
The FAB classification of AML is based on the type of cell from which the leukaemia developed and its degree of maturity.4
M0: acute myeloblastic leukaemia without maturation
M1: acute myeloblastic leukaemia with minimal granulocyte maturation
M2: acute myeloblastic leukaemia with granulocyte maturation
M3: acute promyelocytic leukaemia (APL)
M4: acute myelomonocytic leukaemia
M5: acute monocytic leukaemia
M6: acute erythroid leukaemia
M7: acute megakaryoblastic leukaemia
The WHO classification is more clinically useful and produces more meaningful prognostic information than the FAB criteria.
The mainstay of treatment in AML is chemotherapy. Chemotherapy regimes in AML consist of an induction period, consolidation period, and maintenance therapy.11
Induction chemotherapy is a shorter and more intensive period of treatment that can last from 2-6 weeks.
The goal is to clear the blood of leukemic cells (blasts) and to reduce the number of blasts in the bone marrow to a normal level. This is high-dose chemotherapy that can cause severe side-effects.
Consolidation chemotherapy is given once a patient has recovered from the induction phase.
The aim of consolidation is to kill the remaining blast cells. It is indicated even if there is no evidence of tumour cells remaining after induction.
Consolidation is usually given in cycles and the dosage of chemotherapy is usually lower. Although it is a lower dose, it is still significant and can cause severe side-effects.
Maintenance chemotherapy involves administering a low dose of chemotherapy regularly to maintain remission. This period can last from months up to 2 years.
The most common chemotherapeutic agents used in AML include:
Cytarabine (cytosine arabinoside – ara-C): this is classified as an anti-metabolite12
Daunorubicin (daunomycin) or idarubicin: this is classified as an anthracycline13
All-trans retinoic acid (ATRA) and arsenic are more commonly used in the treatment of acute promyelocytic leukaemia (APML)
Bone marrow transplantation
A bone marrow transplant is also called a stem cell transplant or, more specifically, a hematopoietic stem cell transplant.
For AML these are usually allogenic transplants where stem cells come from another person, called a donor. The donor’s stem cells are given to the patient after the patient has chemotherapy and/or radiation therapy.
Bone marrow transplant is usually indicated in patients with:14
High cytogenetic risks
Lack of complete remission after first induction treatment
High initial leukocyte count
Supportive therapies for AML include:15,16,17,18
Blood cell transfusions: platelet transfusions are performed when platelets fall below < 10 × 109/L. Red cell transfusions are performed when haemoglobin is < 7 or 8 g/dL.
Adequate analgesia and good oral hygiene are essential in the management of mucositis. Oral hygiene agents include Mycostatin and chlorhexidine mouthwash. Parenteral feeding may be considered in patients undergoing hematopoietic cell transplantation.
Antimicrobial prophylaxis: there is an increased risk of developing bacterial, fungal, and viral infections in neutropenic patients. Pneumocystis pneumonia (PCP) prophylaxis with co-trimoxazole is used in certain patients. An anti-viral such as valacyclovir is considered in some patients to prevent re-activation of herpes simplex virus (HSV). Antifungals are also considered. Broad-spectrum antibiotics are used for febrile patients or when an infection is suspected.
Allopurinol: to prevent the build-up of uric acid caused by tumour lysis.
Anti-emetics: used in the prophylaxis and treatment of nausea and vomiting.
AML may be associated with life-threatening complications.
Certain subclassifications of AML have been associated with specific complications (e.g. disseminated intravascular coagulation – DIC) in acute promyelocytic leukaemia (APML). 7,19
Complications of AML include:
Leukostasis (extremely elevated blast cell count): causing respiratory and/or neurologic distress in a patient with AML
Tumour lysis syndrome: when cancer cells break down quickly in the body, levels of uric acid, potassium, and phosphorus rise faster than the kidneys can remove them
Disseminated intravascular coagulation: when proteins that control blood clotting become overactive. This can cause blood clots in small vessels and hypo-perfusion of organs. It can also cause clotting proteins to be consumed, leading to an elevated risk of serious bleeding.
Age is the most significant patient-specific risk factor in acute myeloid leukaemia. For those >60 years old, the prognosis is improving but remains poor.20
The 5-year survival rate for people 20 and older with AML is approximately 25%. For people younger than 20, the survival rate is 67%.21
Acute myeloid leukaemia is a cancer of white blood cells that arises from the uncontrolled growth of the myeloid cell line in the bone marrow.
AML is responsible for about 25% of childhood leukaemia, but it is the most common acute leukaemia in adults.
The most common risk factor for AML is myelodysplastic syndrome and other pre-existing haematological disorders.
Some patients may be asymptomatic with AML while others present with signs and symptoms of anaemia, thrombocytopaenia, neutropenia and leukaemic infiltration.
A diagnosis of AML requires identifying ≥20% myeloid blasts in the bone marrow (or peripheral blood).
Full blood count, LDH, uric acid and peripheral blood smear are the primary investigations. These may be followed by a bone marrow aspirate and biopsy.
The mainstay of treatment in AML is chemotherapy. This regime usually consists of an induction period, consolidation period and maintenance therapy.
Serious complications of AML include leukostasis, tumour lysis syndrome, and disseminated intravascular coagulation.
Dr Kevin Maxwell
Cork University Hospital
Dr Chris Jefferies
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Müller, LP.; Müller-Tidow, C.; The indications for allogeneic stem cell transplantation in myeloid malignancies. Dtsch Arztebl Int. 2015;112(15):262-70.
Hong, CHL.; Gueiros, LA.; Fulton, JS.; Cheng, KKF.; Kandwal, A.; Galiti, D.; et al. Systematic review of basic oral care for the management of oral mucositis in cancer patients and clinical practice guidelines. Support Care Cancer. 2019;27(10):3949-67.
Rajesh V, Lalla.; Stephen T, Sonis.; Douglas E, Peterson.; Management of Oral Mucositis in Patients with Cancer. Dental Clinics of North America. January 2008. p. 61-77.
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