There are two main types of acute leukaemia, myeloid and lymphoblastic. Lymphoblastic leukaemia can also be called lymphocytic leukaemia.
Acute lymphoblastic leukaemia (ALL) is divided into different groups (subtypes). Doctors use two different systems to work out which type a person has. These are the:
- World Health Organisation (WHO) system
- French and British (FAB) system
Ask your doctor which system they are using if you are unsure. The type of ALL you have tells you the type of cell that the cancer started in. Knowing this helps your doctor decide which treatment you need.
Finding the type of ALL
Your doctor looks at your leukaemia cells under a microscope to find out which group your leukaemia is in.
Your doctor also does tests for:
- proteins that some types of leukaemia cells make (immunophenotyping tests)
- chromosome changes in the leukaemia cells (cytogenetic tests)
World Health Organisation (WHO) system
Doctors mostly use the World Health Organisation (WHO) system. It's based on the type of lymphocyte (white blood cell) that has become cancerous and the characteristics the cell has. This system helps your doctors to plan treatment and predict how well the treatment will work. There are 3 different subtypes:
- pre (precursor) B cell ALL, this is the most common type in adults
- pre (precursor) T cell ALL, this is more likely to affect young adults and is more common in men
- mature B cell ALL, this type is identified by particular genetic changes
Mature B cell ALL is sometimes called Burkitt type ALL because it is similar to another cancer called Burkitt lymphoma.
French American British (FAB) system
This is an older system that doctors use less often. It divides ALL into 3 groups (L1, L2 and L3) depending on what the leukaemia cells look like under the microscope.
Mixed phenotypic acute leukaemia (MPAL)
This is a rare type of leukaemia and has a mixture of features from acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML). This might also be called acute biphenotypic leukaemia or acute bilineal leukaemia.
Philadelphia positive ALL
In Philadelphia positive leukaemia you have a particular change in the chromosomes of the leukaemia cells. About 20 to 30 out of every 100 people with ALL (about 20 to 30%) have this change.
Most cells of your body have 23 pairs of chromosomes. Chromosomes are made of DNA. Sections of DNA are called genes. Genes make proteins which have particular jobs to do in the body. For example some genes control how much a cell grows and divides.
When a cell divides to make new cells, the chromosomes normally stay the same. But sometimes mistakes happen.
With Philadelphia positive ALL, a gene called the ABL1 gene on chromosome 9 breaks off and sticks to a gene called the BCR gene on chromosome 22. It produces a new gene called BCR-ABL1 which causes the cell to make too much of a protein called tyrosine kinase. This protein encourages leukaemia cells to grow and multiply.
Doctors treat Philadelphia positive ALL with a targeted cancer drug called imatinib, which blocks this protein.