Leukaemia is a type of blood cancer that usually affects white blood cells and bone marrow. White blood cells are an important part of your immune system that fight infection, and bone marrow is where blood cells like these are made.
There are many different types of leukaemia. Some types develop faster, and are known as acute leukaemia. These include acute lymphoblastic leukaemia (ALL), acute myeloid leukaemia (AML), acute premyelocytic leukaemia (APL), and B or T-cell acute lympoblastic leukaemia.
But each type of leukaemia acts differently, and will need to be treated differently.
Acute promyelocytic leukaemia (APL) is a rare form of acute myeloid leukaemia (AML), and around 200 people in the UK find out they have APL every year. This used to be one of the most deadly blood cancers, but today, thanks to research, most people respond well to treatment. In fact treatment for APL was the first example of a truly targeted treatment for cancer. But there is still more to do.
Neutophils – a type of white blood cell that fights infection – are usually produced from cells called promyelocytes in the bone marrow. In a person with APL, the promyelocytes don’t mature properly and become cancerous. These cancerous cells collect inside the bone marrow, so there isn’t enough room for normal blood cells to be made, causing bruising and bleeding, infections and weight loss.
A distinctive feature of APL is the presence of a ‘fusion gene’ called PML/RARA, and occurs when parts of two chromosomes (chromosomes 15 and 17) swap over. The fusion gene generates an abnormal fusion protein called PML-RARα, which triggers cells to grow out of control and cause APL. Almost all people with APL (around 99% of cases) have this fusion gene in their leukaemia cells.
People with APL are usually treated with a drug called alltrans retinoic acid (ATRA), which targets the PML-RARα fusion protein. ATRA is usually given with chemotherapy. If this approach is unsuccessful, arsenic trioxide (ATO) may be effective, and works in a similar way to ATRA. But while initial treatment for APL can cure many people, others will experience disease relapse, or go on to develop a different type of leukaemia.