Acute promyeloid leukaemia (APML)
Acute Promyelocytic Leukaemia (APML) is a subtype of Acute Myeloid Leukaemia (AML).
APML is most commonly associated with a swapping over (translocation) of chromosomes 15 and 17. This causes parts of a gene from each of these chromosomes to "join" and create a fusion gene called PML/RARA. In some cases, other chromosomes may translocate and cause a variant APML, but this is quite rare. In APML, promyelocytes (an immature type of White Blood Cell) accumulate in the bone marrow, causing a decreased number of normal white blood cells in the blood and reduces production of other types of cells like red blood cells and platelets.
How does APML affect the body?
Many of the symptoms of APML are related to low red blood cells, low white blood cells, low platelets and abnormal clotting factors. These include: anaemia (low red cell count), infection, bleeding and bruising.
Who does APML commonly affect?
APML is equally common in men and women. Age is not a significant factor as there is a fairly constant rate of diagnosis across all age groups after the age of 10 years. There are less than 100 cases of APML diagnosed in Australia each year. It is equally common in males and females.
Do we know what causes APML?
There are no clear factors identified as causing the development of APML. People who have had previous treatment with chemotherapy or radiotherapy can develop "treatment related" APML, but this is relatively uncommon. Occasionally, some types of bone marrow diseases may increase the risk of developing "secondary APML".
How is APML treated?
All Trans Retinoic Acid (ATRA) is a medication given for the treatment of APML (for those who have the PML-RARA fusion gene present in their APML) and is commenced as soon as the diagnosis is suspected. It is not a chemotherapy agent, but works by overcoming the immature promyelocyte cells' inability to absorb retinoic acid (a compound required for cell growth and development). ATRA enables these promyelocytes to develop and then die as would normally happen.
Chemotherapy agents and a medication called Arsenic trioxide (ATO) are also used in the treatment of APML. The first cycle of treatment a patient receives is called induction therapy.
Patients with APML have an increased risk of developing Disseminated Intravascular Coagulation (DIC). This is a serious condition where clots form in blood vessels whilst causing a decrease in the production of clotting factors and thereby increasing the risk of bleeding. This condition is managed through regular blood tests, often twice daily, to monitor platelet and clotting levels, and the transfusion of blood products like Red Blood Cells, Platelets and clotting factors.
Patients with APML have a higher incidence of presenting with a life threatening bleeding abnormality than those with Acute Myeloid Leukaemia (AML), therefore starting treatment when APML is suspected is important.
Retinoic Acid (RA) Syndrome can sometimes develop after initial treatment and is thought to be a side effect of the chemical processes that occur after treatment with ATRA. Patients receiving ATRA will be monitored for signs of lung or breathing problems.
Further cycles of chemotherapy will be given after the initial induction treatment. This is called consolidation therapy and is an important part of minimising the chances of the APML returning (relapse) and can last for up to two years.
Although not routinely used, stem cells transplants may sometimes be considered for patients who have relapsed after initial induction therapy.
*Please note that the treatments described above are for patients who have the PML-RARA fusion gene present in their APML. Treatments for the less common subtype differ significantly.