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Acute promyelocytic leukaemia (APL) is a blood cancer, which affects the myeloid cells, which include red blood cells, platelets and some white blood cells. APL is a rare sub-type of acute myeloid leukaemia (AML). When you have APL, the bone marrow is not able to make enough normal blood cells.
APL is treated in a very different way from other forms of AML, if a patient with APL is given standard treatment, there is a risk of serious problems with their clotting system. Fortunately, it is usually very easy to tell the difference between APL and other types of AML.
Acute promyelocytic leukaemia usually responds very well to treatment and patients with this form of leukaemia have a good chance of being cured.
The cause of most cases of APL are not known. It is sometimes seen in people who have been treated for other forms of cancer; this only affects a very small percentage of cancer patients. This is known as therapy-related APL (t-APL) and accounts for about 1 in 10 cases of APL; this type of APL is treated in the same way as other cases and responds equally well to treatment. You cannot catch APL from someone who has it and you cannot pass APL on to your children.
The most common symptoms and their causes are:
APL is diagnosed by tests which may include:
Other tests may be done
Occasionally, it is not clear from the blood film whether the abnormal cells are promyelocytes. By examining the proteins found on the outside of the cell, called cell markers, it is possible to identify the cells with certainty.
Another test looks for an abnormality called PML-RARA. This is an abnormal “fusion gene” – PML and RARA are two genes which are normally found on different chromosomes. In APL the two chromosomes swap over part of their DNA, which joins the PML and RARA genes together. This test is important because the main drugs used to treat APL work directly on the PML-RARA gene; in the very rare cases of APL without PML-RARA, other treatments can be used.
These tests may be repeated from time to time during your treatment. This is to find out how the APL is responding to treatment.
It is normal to start treatment as soon as possible when you are diagnosed with APL. This is because, until you have started treatment, there is a risk of a serious, possibly fatal bleed. Most patients respond very well to treatment but it is vital to start this as soon as possible.
Unlike other kinds of leukaemia, most patients with APL start treatment before all of the tests have been done. This is partly because it is necessary to start treatment without delay, but also because if a patient with APL is given standard AML treatment, there is a very high risk of a life-threatening bleed. Fortunately, in the very rare cases where the diagnosis is changed after starting APL treatment, the treatment already received will do no harm. If you have any concerns, contact your haematologist.
The standard first line treatment for APL involves all-trans retinoic acid (ATRA), which is similar to vitamin A, and Anthracyclines (Anthracyclines are a group of chemotherapy drugs). ATRA blocks the effects of the PML-RARA gene. When the abnormal gene is blocked the cells continue to develop – this is called differentiation. ATRA and Anthracyclines may be given at the same time (normally if you have a high white blood cell count at the time of diagnosis), or the Anthracyclines may be introduced a few days after the treatment with ATRA is started. ATRA is usually given in the form of tablets, while Anthracyclines are given intravenously (directly into a vein).
Second line treatment is used for patients who haven’t gone into remission or who have relapsed. This treatment is usually a combination of ATRA and arsenic trioxide (ATO). ATO is also sometimes used in first line treatment if the patient is not suitable for chemotherapy. It is also sometimes used in clinical trials.
Treatment also involves blood and platelet transfusion, along with plasma. Platelet counts are kept higher with platelet transfusion in APL compared to other AMLs.
ATRA may cause a side effect called differentiation syndrome (DS). When DS does happen it can usually be dealt with by steroid treatment. APL treatment only has to be reduced or suspended if DS is very severe, which is very rarely the case.
There is a very good chance that standard treatment will cure APL.