Treatment of Acute Promyelocytic Leukemia (APL)

Prompt diagnosis and treatment of acute promyelocytic leukemia (APL), the M3 subtype of acute myeloid leukemia (AML), is very important because patients with APL can quickly develop life-threatening blood-clotting or bleeding problems if not treated. In fact, treatment might need to be started even if the diagnosis of APL is suspected but hasn't been confirmed yet by lab tests.

The treatment of APL typically differs from the treatment of most other types of AML. The most important drugs for treating APL are non-chemo drugs called differentiating agents, like all-trans-retinoic acid (ATRA). Other treatments might include chemotherapy (chemo) and transfusions of platelets or other blood products.

Treatment is typically divided into 3 phases:

• Induction (remission induction)
• Consolidation (post-remission therapy)
• Maintenance

Induction

The goal of induction, the first part of treatment, is to get the number of leukemia cells to very low levels, putting the APL into remission. The most important drug in the initial treatment of APL is all-trans-retinoic acid (ATRA). This is usually combined with one of these:

• Arsenic trioxide (ATO), another non-chemo drug. For some people at higher risk of APL coming back after treatment, the targeted drug gemtuzumab ozogamicin (Mylotarg) might be added as well.
• Chemotherapy with an anthracycline drug (daunorubicin or idarubicin). For some people at high risk of their APL coming back after treatment, the chemo drug cytarabine (ara-c) might be added as well.
• Chemotherapy (an anthracycline) plus ATO

ATRA plus ATO is often the preferred treatment in people at lower risk of the leukemia coming back, as it tends to have fewer side effects. Chemo or Mylotarg is more likely to be included in treatment if this risk is higher.

A bone marrow biopsy is usually done about a month after starting treatment, to see if the leukemia is in remission. Induction is typically continued until the APL is in remission, which might take up to 2 months.

Consolidation (post-remission therapy)

Once APL is in remission, consolidation is needed to keep it in remission and try to get rid of the remaining leukemia cells. Which drugs are used depends on what was given for induction, as well as other factors. Patients typically get some of the same drugs they got during remission, although the doses and timing of treatment might be different. Some of the options include:

• ATRA plus ATO (If Mylotarg was part of induction, it might be continued here as well.)
• ATRA plus chemo (typically with an anthracycline such as idarubicin or daunorubicin)
• ATO plus chemo (typically with an anthracycline such as idarubicin or daunorubicin)
• Chemo alone (typically with an anthracycline plus cytarabine)

Consolidation typically lasts for at least several months, depending on the drugs being used.

Maintenance

For some patients, especially those at higher risk of the APL coming back, consolidation may be followed by maintenance therapy, which uses lower doses of drugs over a longer period of time. People who have a lower risk of the leukemia coming back and who have a good response to ATRA plus ATO might not need maintenance therapy, although this is still being studied.

The most common options for maintenance therapy are ATRA alone, or ATRA along with chemo (6-mercaptopurine (6-MP) and/or methotrexate). Maintenance therapy is typically given for about a year.

Treating APL that doesn't go away or comes back

Treatment for APL that doesn't go away or that comes back after initial treatment is discussed in If Acute Myeloid Leukemia (AML) Doesn't Respond or Comes Back After Treatment.