In leukaemia abnormal blood cells divide uncontrollably. They have no useful function and crowd out the bone morrow preventing the development of normal blood cells. Sometimes, there are so many in the bone marrow that they also spill out into the blood circulation

The main types of leukaemia and their major characteristics are:

• acute leukaemias
  • develop quickly and progress rapidly (over weeks)
  • involve mainly large numbers of immature cells (blasts)
  • need prompt treatment.
     
• chronic leukaemias
  • develop and progress more slowly (over months)
  • involve more mature but still abnormal blood cells
  • may not need treatment when diagnosed.

Chronic leukaemia usually develops slowly over months to years. There are 2 main types of chronic leukaemia.

Chronic lymphocytic leukaemia (CLL)

This is a cancer of white blood cells called lymphocytes.

There are several different ways to stage CLL. One system commonly used in Australia is the ABC or Binet staging system. This divides CLL into 3 stages based on the person’s clinical features and blood test results:

• stage A – early disease with a high number of white blood cells but minimal enlargement of lymph nodes.
• stage B – intermediate disease with a high number of white blood cells and enlarged lymph nodes in 3 or more areas.
• stage C – late disease with a high number of white blood cells, enlarged lymph nodes, and a low number of platelets and red blood cells. The liver and/or spleen may also be enlarged.

Chronic myeloid leukaemia (CML)

This type of leukaemia starts in white blood cells known as granulocytes.

CML has 3 phases:

• chronic – early disease where white blood cell counts are relatively stable - this phase can last for years
• accelerated – when the white blood cell counts start to rise and other abnormalities may develop
• blast phase – rapidly progressive disease with a high number of blasts in the blood that can cause many symptoms. This phase of CML behaves like acute leukaemia.