Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML). APL cells have a very specific abnormality that involves chromosomes 15 and 17, leading to the formation of an abnormal fusion gene called PML/RARα. This mutated gene causes many of the features of the disease. APL accounts for about 10-15 percent of all adult AML cases diagnosed each year.
Promyelocytes are immature white blood cells. In APL, these cells are overproduced and accumulate in the bone marrow. Signs, symptoms and complications of APL result from the overproduction of promyelocytes and the underproduction of healthy blood cells.
Treatment for patients with acute promyelocytic leukemia (APL) differs from treatment for patients with other AML subtypes. Because of advances in diagnosis and treatment of this disease, APL is now considered the most curable form of adult leukemia. Cure rates of 90 percent have been reported from centers specializing in APL treatment.
Treatment decisions are based on the patient’s age, general health and APL risk classification. APL is classified into the two following categories of risk, based on the patient’s white blood cell count at diagnosis:
- Low risk—white blood cell (WBC) count of 10,000 white blood cells per microliter of blood (10,000/microliter) or less
- High risk—WBC count greater than 10,000/microliter
Typically, patients with low-risk disease are treated with less intensive regimens than those used for patients at high risk. Pediatric patients are often treated with the same or very similar regimens as those used for adult patients.
Treatment of APL is divided into three phases, each with its own objectives.
- Induction therapy starts immediately after diagnosis with the goals to kill as many APL cells as possible, bring blood cell counts to normal levels, and decrease APL-related symptoms. This is known as a complete hematologic response (CHR).
- Consolidation therapy follow induction therapy. Its main goal is to convert the CHR into a remission.
- Maintenance therapy aims to ensure that remission is maintained over time.
Click below to read more about APL treatments:
- All-trans retinoic acid
- Arsenic trioxide
- Stem cell transplantation
- Clinical trials
All-trans retinoic acid (ATRA), also called tretinoin (Vesanoid®), is given orally. This drug, a vitamin A derivative, has become a standard component of induction therapy for APL. ATRA targets and eliminates the PML/RARα abnormality. This treatment causes a marked decrease in the concentration of leukemic blast cells in the marrow, and a remission frequently follows. Used alone, ATRA can induce a short-term remission in at least 80 percent of patients. Treatment with ATRA must be followed by or given with arsenic trioxide (ATO) and/or chemotherapy to ensure that the remission will be long-lasting. ATRA often minimizes the side effects of chemotherapy because blood cell counts may be improved and the number of leukemic cells may be decreased at the time that chemothearpy is started.
Aresenic Trixoide (Trisenox®) is given by slow intravenous (IV) injection. Studies have shown that the combination of ATO and ATRA is superior to the former standard of care, which included anthracyclines (chemotherapy), for patients with low-risk APL. Avoiding additional chemotherapy drugs may be particularly beneficial to children and older patients who are more susceptible to the side effects of anthracyclines.
The combination of arsenic trioxide with tretinoin has been FDA-approved for the treatment of adults with newly diagnosed low-risk APL characterized by the presence of the t(15;17) translocation or PML/RARα gene expression. Sometimes ATO is administered daily, and other times it is given only on certain days with rest days in between as part of what is called a “treatment cycle.”
ATO is also the recommended therapy for patients who do not achieve a molecular response at the end of consolidation or who relapse later in the treatment. For patients with high-risk APL, combinations of ATO, ATRA, and anthracyclines are commonly used.
These chemotherapy agents interact directly with the DNA in the nucleus of leukemic cells, interfering with cancer cell survival. There are several types of anthracyclines; daunorubicin (Cerubidine®) and idarubicin (Idamycin®) are the drugs most commonly used in the treatment of APL, typically in combination with ATRA. The initial remission rate of APL patients treated with ATRA and an anthracycline, such as idarubicin, is about 90 percent. The combination of ATRA and idarubicin is known as AIDA.
These chemotherapy agents prevent leukemic cells from growing by substituting for their DNA or RNA building blocks. For people with high-risk APL (white cell counts greater than 10,000/microliter at diagnosis), the antimetabolite cytarabine (Cytosar-U®) may be added to induction or consolidation regimens. Cytarabine (also called Ara-C or cytosine arabinoside) is sometimes given with ATRA and an anthracycline.
A small number of APL patients have persistent minimal residual disease (MRD) at the end of consolidation therapy. These patients may benefit from arsenic trioxide (Trisenox®) or GO (gemtuzumab ozogamicin), followed by autologous or allogeneic stem cell transplantation.
For information about the drugs listed on this page, visit Drug Listings.
Approaches under study in clinical trials for the treatment of APL include
- Oral arsenic trioxide (ATO)
- Gemtuzumab ozogamicin (GO) (Mylotarg®)
- Chemotherapy-Free Regimen for Pediatric Patients
- Patient Care Strategy Study to Decrease Patient Mortality in APL
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Side Effects and Supportive Care
APL treatment can cause unwanted and unpleasant side effects. Side effects may be caused by the drug type and dose used, length of treatment and the patient’s overall health. Management of side effects is important. If you have any concerns about your side effects, talk to your doctor to get help. Most side effects are temporary and resolve when treatment is completed. However, patients with APL may need specific kinds of supportive care. See Acute Promyelocytic Leukemia Facts to learn more.
- Download or order The Leukemia & Lymphoma Society's free fact sheet, Acute Promyelocytic Leukemia Facts.
- For information about the drugs mentioned on this page, visit Drug Listings.