Lymphoblastic leukaemia

• Acute leukaemia is classified into two main types; acute lymphoblastic leukaemia and acute myeloid leukaemia.
• ALL occurs in both children and adults but is more common in young children, peaking in incidence between the ages of 2 and 5 years.
• When a patient is diagnosed with either acute lymphoblastic leukaemia, further classification of the subtype of leukaemia is central to decisions made on the most appropriate treatment schedule.
• Identifying patients into risk categories (high, medium, low) is an important aspect of the diagnosis process with acute leukaemia.

Acute lymphoblastic leukaemia occurs in both children and adults, and two patterns of incidence occur. Acute lymphoblastic leukaemia is more common in young children, peaking in incidence between the ages of 2 and 5 years (Pui et al, 2008). It is rare under 1 year of age, and infants under 1 years old have poorer outcomes than older children with acute lymphoblastic leukaemia (Pieters et al, 2007).

The incidence of acute lymphoblastic leukaemia is higher in males than females across all age groups. However, children have fared better from improved treatment regimens than adults (Faderl et al, 2010). The 5-year event-free survival rate for childhood ALL is around 80% and almost 90% for the 5-year survival rate (Pui, 2010).

Classification

Clinical classification of acute lymphoblastic leukaemia concentrates on the differentiation of T and B lymphocytes, and the World Health Organisation (WHO) classification (Vardiman, 2010) outlined two principal classifications of ALL:

Patients with acute leukaemia present with variable features. A significant rise in the white blood count is a typical sign of acute leukaemia, but pancytopenia (neutropenia, anaemia and thrombocytopenia) (O’Donnell, 2004) is a frequent presentation. It is common for people with acute lymphoblastic leukaemia to experience a myriad of systemic symptoms, such as tiredness, fever, recurrent infections, bone discomfort, swollen lymph nodes, enlarged spleen and loss of appetite or weight loss.

Organ infiltration by lymphoblasts may also occur (Atkinson and Richardson, 2006). The central nervous system is one of the most frequent locations of leukaemic infiltration. In addition, bone pain is present in 40–50% of children with acute lymphoblastic leukaemia, but only occurs in 5–10% of adults with acute leukaemia (O’Donnell, 2004).  

When acute lymphoblastic leukaemia is suspected, many tests are undertaken to confirm the diagnosis. These tests include bone marrow aspirate and trephine biopsy, immunophenotyping and cytogenetics (Atkinson and Richardson, 2006). Bone marrow aspiration is a procedure where some bone marrow fluid is removed, and spread on slides in preparation for examination in the laboratory. A bone marrow trephine biopsy involves the removal of a core from the bone, including marrow. The bone marrow aspirate and biopsy are performed to determine the blast percentage and assess, on grounds of appearance (morphology), whether the leukaemia is more likely to be acute lymphoblastic leukaemia or acute myeloid leukaemia. A critical threshold of 20% blasts in the bone marrow is required to diagnose acute leukaemia.

Immunophenotyping and cytogenetics are performed on the bone marrow aspirate sample. Immunophenotyping is performed using a flow cytometer following incubation of leukaemia cells with a panel of different fluorescein-labelled

The aim of acute lymphoblastic leukaemia treatment is to destroy the leukaemia cells and to eventually eradicate the leukaemic stem cell population, allowing permanent repopulation of the bone marrow by healthy, normal bone marrow cells. Prior to commencing treatment, many factors have to be considered, including the patient’s age and general health, the patient's and family's wishes, type of lymphocyte involved, presence of Philadelphia chromosome, and whether the disease is refractory (has not responded to first-line treatment) or relapsed (has been treated previously for the disease).