What is acute promyelocytic leukaemia (APL)?

Updated 10 Aug 2017

Acute promyelocytic leukaemia (APL) is a form of cancer that affects blood-producing cells in the bone marrow. It occurs when these cells don’t mature properly and become cancerous. APL is a subtype of acute myeloid leukaemia (AML).

In this section you can find out more about how APL develops.

What is acute promyelocytic leukaemia (APL)?

When you’re healthy and everything is working normally, the promyelocytes in your bone marrow mature and produce neutrophils (cells which fight infections).

In a person with APL, the promyelocytes don’t mature properly and become cancerous. These cancerous cells collect inside the bone marrow, which means there isn’t room for enough normal blood cells to be made. This is what causes most of the symptoms of APL.

All kinds of cancer involve changes in genes in the affected cells. The distinctive feature of APL is the presence of a faulty gene called PML/RARA. Almost all people with APL (around 99% of cases) have this faulty gene in their leukaemia cells.

The PML/RARA gene is caused by parts of two chromosomes (chromosomes 15 and 17) swapping over. This is called a translocation. When you are being diagnosed, your doctors will look at the chromosomes in your bone marrow to check for this translocation.

What causes APL?

In many cases, we still don’t know what causes APL. There are no known environmental factors which have been proven to increase the risk of getting APL. You may have a slightly increased risk of getting APL if you’ve been treated for a different cancer or if you’ve received chemotherapy for another condition in the past.


You can get APL at any age. It’s slightly less common in children under 10, but otherwise the likelihood of developing APL is roughly the same across all age groups.


APL is equally common in men and women.

Family history

We don’t know of any reported evidence of APL running in families. Occasionally, there are cases where another family member may also have leukaemia or another type of blood cancer, but the cause of this may not be inherited.

Receiving treatment for other cancers

A very small number of patients can develop APL after being treated for another cancer or treatment with chemotherapy for another condition. This type of APL is called treatment related APL (tAPL) and can be caused by certain types of chemotherapy or radiotherapy.

More than half of all cases of tAPL occur in people who have previously been treated for breast cancer, but the overall risk of developing tAPL is still very low. The risk of developing tAPL is highest in the three years after the treatment for the previous cancer.

The treatment for tAPL is generally the same as for other forms of APL, although your specialist may choose to use a different drug in this situation.

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