Leukaemia occurs when the blood-making cells, which reside in our bone marrow (the soft tissue inside our bones), grow abnormally.¹

There are three types of blood cells; red blood cells (which deliver oxygen to the body), white blood cells (which help fight infection) and platelets (which help the blood to clot and prevent us from bleeding). ¹

Leukaemia typically affects the white blood cells. There are four main types of leukaemia (although there are many sub-types), depending on what type of white blood cell is affected (either myeloid or lymphoid) and whether it is fast growing (acute) or relatively slow growing (chronic).⁴

Acute and chronic classifications do not reflect how serious the disease is, but the rate of progression. Acute leukaemia develops and progresses rapidly, while chronic leukaemia appears gradually and is slow growing over months to years.

Due to the rapid nature of acute leukaemia treatment usually begins quickly after diagnosis. Chronic leukaemia may not require treatment for a long time after it is diagnosed.

Acute leukaemia

Healthy bone marrow produces immature white blood cells, called blast cells. These blast cells then develop into mature white cells, red cells and platelets, and are eventually released into the blood stream.

In people with acute leukaemia, the diseased bone marrow produces an excessive number of abnormal blast cells, called leukaemic cells. These immature cells accumulate in the bone marrow interfering with the production of normal blood cells.

Common forms of acute leukaemia:

• Acute lymphoblastic leukaemia (ALL) – affects immature cells called lymphoblasts. This type of leukaemia develops quickly.⁵ Most ALL occur in children under four years of age. ⁵
• Acute myeloid leukaemia (AML) – affects immature cells called myeloblasts. It is the most common form of acute leukaemia in adults.⁶

Chronic leukaemia

In chronic leukaemia there is a build-up of mature but abnormal white blood cells that have undergone a malignant change when developing from a blast cell.

Common forms of chronic leukaemia are:

• Chronic lymphocytic leukaemia (CLL) – the most common type of leukaemia in western countries. Predominantly affects older people and is often very slow growing.⁷
• Chronic myeloid leukaemia (CML) – typically grows slowly in the early phases but can transform to acute leukaemia.³

Acute Lymphoblastic Leukaemia (ALL)

There is no standard staging system for ALL.⁴ Rather, laboratory tests (such as blood and bone marrow tests) can determine the subtype of ALL, which is based on the World Health Organisation (WHO):¹³

• Pre-B cell ALL – early stage development of leukaemia in the bone marrow
• B-cell ALL – is found in developed, or more mature lymphoid cells
• T-cell ALL – leukaemia is found in developing T-cells

Chronic Lymphocytic Leukaemia (CLL)

Most Australian doctors use what is called the Binet staging system to classify CLL. (The other system also used is known as the Rai system is more commonly used in the United States).¹²

The Binet system classifies CLL into three stages: ¹²

• Stage A – increased white blood cell count but < 3 enlarged lymph nodes
• Stage B – increased white blood cell count and >3 enlarged lymph nodes
• Stage C – increased white blood cell count and low red cell and/or platelets

Acute Myeloid Leukaemia (AML)

There is no staging system for AML.⁴ Rather, based on laboratory testing (including genetic testing) AML can be classified into a subgroup, which then has an effect outcome.¹⁴

Chronic Myeloid Leukaemia (CML)

There are three stages of phases of CML:

• Chronic phase – this stage can last many years and is characterised by relative clinical stability. Blast cell numbers in the blood and bone marrow are low (< 5%)¹⁵
• Accelerated phase – during this period the number of blast cells start to increase in the bone marrow and blood ¹⁵
• Blast phase – is a period of rapid progression and the disease is similar to acute leukaemia. Blast cell numbers in the blood and bone marrow increase rapidly¹⁵