Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia (AML). This subtype of AML is treated with different medicines than other types of AML. This is because the leukemia cells in APL are often very sensitive to medicines called differentiating agents. APL is one of the most curable forms of leukemia.

Differentiating agents are medicines. They’re not the same as standard chemotherapy medicines. Chemotherapy normally works by killing cells that grow quickly, such as leukemia cells. But differentiating agents don’t kill the leukemia cells. Instead, they cause them to change (differentiate) into more mature cells, so they are no longer leukemia cells.

These medicines work differently from standard chemotherapy. So they tend to have different and often less severe side effects.

The medicines that can be used to treat APL are:

• All-trans retinoic acid (ATRA). This is also known as tretinoin. This medicine is a form of vitamin A.

• Arsenic trioxide (ATO). This medicine is a form of the chemical arsenic.

These medicines may be used alone or together. In some cases, they may be used along with certain chemotherapy medicines. They are not used to treat other subtypes of AML.

Differentiating agents are part of the standard treatment for all people with APL. ATRA is taken daily as a pill. ATO is given daily as an IV (intravenous) injection into a vein. Here is an example of how these medicines may be used to treat APL:

• Induction. This is the first phase of treatment. The goal is to try to put APL into remission. Remission is when there are no signs of leukemia in the body. In this phase, ATRA is often given along with either a chemotherapy medicine and/ or with ATO.

• Consolidation. This second phase is used to keep the leukemia in remission. This phase often lasts for several months. The medicines used are often the same as those used for induction.

• Maintenance. Some people may continue to take ATRA for up to a year to keep any leukemia cells under control. The goal is to maintain the remission. Sometimes chemo medicines drugs may be given, too.

ATO can also be used if the leukemia comes back (relapses) after treatment with ATRA. Or it can be used for leukemia that doesn't go into remission by the end of consolidation.

The possible side effects of ATRA include:

• Fever

• Headache

• Feeling tired and weak

• Bone pain

• Skin rash

• Dry skin, dry mouth, or cracking at the corners of the mouth

• Nausea and vomiting

• Sores in the mouth and throat

• Eye irritation

The possible side effects of ATO include:

• Feeling tired

• Fever

• Nausea or vomiting

• Swelling

• Diarrhea

• Belly pain

• Nerve damage (neuropathy), which can cause numbness, tingling, or pain in the hands or feet

• Changes in heart rhythm

In the first few weeks of treatment, these medicines can sometimes cause a group of side effects known as differentiation syndrome. This syndrome can be life threatening. Symptoms can include:

• Fever

• Breathing problems or cough due to fluid in the lungs

• Low blood pressure

• Irregular heart beat 

• Severe fluid retention

If you have symptoms of differentiation syndrome, your doctor may prescribe steroids or have you stop treatment for a few days.

It's important to know which medicines you're taking. Write your medicines down, ask your healthcare team how they work, and what side effects they might have.

Talk with your healthcare providers about what side effects to watch out for, and when to call them. Make sure you know what number to call with questions, even on evenings and weekends.

It may be helpful to keep a diary of your side effects. Write down physical, thinking, and emotional changes. A written list will make it easier for you to remember your questions when you go to your appointments. It will also make it easier for you to work with your healthcare team to make a plan to manage your side effects.