Acute myeloid leukaemia

Acute myeloid leukaemia (AML), also referred to as acute myelogenous leukaemia, is a haematological malignancy characterised by the abnormal clonal proliferation of immature myeloid precursors (myeloblasts) or poorly differentiated cells of the haematopoietic system. It primary infiltrates the bone marrow, but the disease can also extend to blood and other tissues.

Epidemiology

It is more common in middle-aged and elderly patients, with a median age of diagnosis at 70 years. The M:F rate varies from 1.1 in the 5^th decade to about 1.8 in the 8^th decade of life ^2,3. 

Acute myeloid leukaemia only accounts for ~20% of all childhood leukaemias, cf. acute lymphoblastic leukaemia (ALL), which represents ~80% of leukaemias at this age group ². 

There is an ethnic component in the distribution of most types of acute myeloid leukaemia, with a strong predominance among the white ethnicity group ^2,3.   

Risk factors   

• therapy-related acute myeloid leukaemia (t-AML)

  • immunosuppression for a solid organ transplant

  • prior radiation therapy or chemotherapy  

• trisomy 21 ⁸

Clinical presentation 

Acute myeloid leukaemia tends to present with vague and non-specific symptoms such as fatigue and is most commonly revealed on full blood count tests, where anaemia, thrombocytopenia, and/or neutropenia are demonstrated ^2,4. 

Described symptoms associated with bone marrow failure include ⁴:

• fevers

• bleeding gums

• multiple ecchymoses

• dyspnoea on exertion

• anginal chest pain

• refractory upper respiratory infection symptoms

Extramedullary leukaemic infiltration can lead to organ-involved signs such as hepatosplenomegaly, leukaemia cutis, lymphadenopathy, gingival hyperplasia, and neurological symptoms ⁴.

Pathology

Location

The leukaemic myeloblasts can commonly be identified either in peripheral blood smears or bone marrow aspirate. Eventually, there is infiltration of other organs and tissues:

• CNS manifestations

• pulmonary manifestations

  • pulmonary complications tend to be observed more frequently at presentation in neutropenic AML patients of advanced age ⁷

• testicular manifestations

Classification

The 2022 World Health Organizatiοn (WHO) classification of haematolymphoid tumours classifies AML into multiple subtypes ⁵. 

Depending on the type of cell lineage involved, AML can be divided into specific morphologic subgroups. 

Microscopic appearance

The leukaemic cells are characterised by very little cytoplasm, which holds fine azurophilic granules and Auer bodies or rods. Irregular nuclei and distinct nucleoli are also features of those cells ⁴.

Treatment and prognosis

Acute myeloid leukaemia has an overall poor prognosis compared to the other main types of leukaemia, having ~30% 5-year survival rate ⁸. This is most evident among elderly patients over 65 years, where up to 70% die within 1 year of diagnosis ⁸.