Overview
The first factor in classifying a patient's leukaemia is whether most of the abnormal cells are mature (look like normal white blood cells) or immature (look more like stem cells).
In acute leukaemia (AML or ALL), the bone marrow cells cannot mature properly. Immature leukaemia cells continue to reproduce and build up. Without treatment, most patients with acute leukaemia would live only a few months.
Some types of acute leukaemia respond well to treatment, and many patients can be cured. Other types of acute leukaemia have a less favourable outlook. 
In chronic leukaemia (CML or CLL), the cells can mature partly but not completely. These cells may look fairly normal but they are not. They generally do not fight infection as well as normal white blood cells. And they survive longer, build up, and crowd out normal cells. Chronic leukaemia's tend to progress over a longer period of time, and most patients can live for many years. But chronic leukaemia's are generally harder to cure than acute leukaemia's.
The second factor in classifying leukaemia is the type of bone marrow cells that are affected.
Leukaemia starts in early forms of myeloid cells -- white blood cells (other than lymphocytes), red blood cells, or platelet-making cells (megakaryocytes) -- are myeloid leukaemias (also known as myelocytic, myelogenous, or non-lymphocytic leukaemias).
If the cancer starts in early forms of lymphocytes, it is called lymphocytic leukaemia (also known as lymphoid or lymphoblastic leukaemia). Lymphomas are also cancers that start in lymphocytes. But whereas lymphocytic leukaemias develop from cells in the bone marrow, lymphomas develop from cells in lymph nodes or other organs. By considering whether leukaemias are acute or chronic and whether they are myeloid or lymphocytic, they can be divided into 4 main types. Find out more from the links below:
- Acute myeloid (or myelogenous) leukaemia (AML)
- Chronic myeloid (or myelogenous) leukaemia (CML)
- Acute lymphocytic (or lymphoblastic) leukaemia (ALL)
- Chronic lymphocytic leukaemia (CLL)
