There are different sub-types of ALL based on the type of lymphocyte (either B- or Tlymphocyte) that has become cancerous.

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

• early (precursor) B-lymphoblastic leukaemia (most adults with ALL have this type)
• mature B-lymphoblastic leukaemia (sometimes called Burkitt-type ALL because it is similar to Burkitt's lymphoma)
• early (precursor) T-lymphoblastic leukaemia.

Philadelphia chromosome

Some people with ALL have a particular genetic abnormality known as a Philadelphia chromosome. The Philadelphia chromosome develops when part of chromosome 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. The protein causes the production of an enzyme called tyrosine kinase, which makes the bone marrow produce abnormal blood cells.

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