Erythroleukaemia is a type of leukaemia.

Years ago doctors thought there were just two types of leukaemia - fast growing (acute leukaemia) and slow growing (chronic leukaemia). Then they realised that there were different types of acute and chronic leukaemia depending on whether the sort of white blood cell that was cancerous was either a lymphocyte (causing acute or chronic lymphatic leukaemia, ALL or CLL) or a myelocyte (causing acute or chronic myelocytic leukaemia, AML or CML).

Nowadays the picture is even more complicated as it is known that there are different types of ALL, CLL, AML and CML!

Erythroleukaemia is a subtype of acute myelocytic leukaemia AML M6.

Doctors group the different types of AML by looking at the cells in the blood and bone marrow under the microscope. The cells they are looking for include:

• blasts: cells which are obviously leukaemic
• promyelocytes cells which form a very early stage in the development of white blood cells
• normal bone marrow cells which are developing into neutrophils (a type of white blood cell)
• normal bone marrow cells which are developing into monocytes (another type of white blood cell)
• normal bone marrow cells which are developing into the red cells of the blood. These cells are called erythrocytes. It is these that are affected in erythroleukaemia.
• normal bone marrow cells which are developing into the platelets in the blood.

Using the results of these cell counts, 8 different types of AML have been described. These are:

• M0 a type of AML that is so primitive and immature that it can only be diagnosed using very specialised tests
• M1 - nearly all the cells are blasts with very few other cells
• M2 - there are blasts but also white cells developing into neutrophils
• M3 - there are lots of cells called promyelocytes
• M4 - there are blasts but also some white cells developing into neutrophils and some developing into monocytes.
• M5 - there are blasts but also white cells developing into monocytes.
• M6 - there are blasts but also lots of cells developing into red cells.
• M7 - there are blasts but also lost of cells developing into platelets.

Erythroleukaemia, AML M6, is mainly a disease of adults and makes up about I in every 20 cases of AML. M6 may appear out of the blue but often it may develop from a previous bone marrow problem such as myelodysplasia.

Treatments for these different groups of AML, except M3, are the same. M0, M6 and M7 tend to have a poorer outcome and M2 and M4 tend to have a better outcome. M3 is a unique category with its own problems and its own treatment.