Classification of acute lymphoblastic leukaemia

The World Health Organisation (WHO)’s classification system is used for planning treatment and predicting response. The three different sub-types of ALL are:

• early (precursor) B-lymphoblastic leukaemia (most adults with ALL have this type)
• mature B-lymphoblastic leukaemia
• early (precursor) T-lymphoblastic leukaemia.

Chromosome abnormalities

Philadelphia chromosome

Some people with ALL have a particular genetic abnormality within the leukaemia cells known as a Philadelphia chromosome.When this chromosome is present, it is sometimes called Philadelphia positive ALL (Ph+ ALL).

The Philadelphia chromosome develops when part ofchromosome 9 (the ABL gene) wrongly attaches to chromosome 22 (the BCR gene) during cell division.

This creates a new gene, known as BCR-ABL, which produces a specific new protein. This protein causes the production of an enzyme called tyrosine kinase, which makes the bone marrow produce abnormal blood cells. Knowing that the Philadelphia chromosome is present means that you can be treated with drugs called tyrosine kinase inhibitors.

The Philadelphia chromosome isn’t inherited and can’t be passed on to your children.

Other chromosome abnormalities 

There may also be other chromosome abnormalities present within the leukaemia cells. These are less common than the Philadelphia chromosome, but may affect how well treatment works.

Your doctors will check for the different abnormalities. Knowing if any chromosome abnormalities are present will help them plan you treatment. Your doctors can discuss this with you further.