Acute Promyelocytic Leukemia
Treatment for patients with acute promyelocytic leukemia (APL), the M3 subtype of acute myeloid leukemia (AML), differs from treatment for patients with other AML subtypes. APL is one of the most frequently cured AML subtypes.
APL affects marrow cells called promyelocytes, which form after myeloblast development. The promyelocytes have abnormal chromosome changes, usually an exchange (translocation) of pieces of chromosomes 15 and 17.
Drugs commonly used to treat APL are:
- all-trans retinoic acid
- arsenic trioxide
All-Trans Retinoic Acid
All-trans retinoic acid (ATRA), a substance that comes from vitamin A, often brings APL into remission. ATRA is also known as tretinoin. Retinoic acid helps the promyelocytes affected by APL develop into fully functioning cells (neutrophils). This process reduces the number of leukemic blast cells in the marrow. And since ATRA also helps improve blood cell counts, it often lessens chemotherapy's side effects.
At least 80 percent of patients undergo short-term remission when ATRA is used alone. For long-lasting remission, ATRA treatment is combined with chemotherapy during or after induction therapy. For APL patients who have a white cell count of 10,000 per microliter or greater when they're diagnosed, the chemotherapy drug cytarabine is sometimes added during induction or postremission therapy.
About 70 percent to 80 percent of APL patients go into remission after being treated with ATRA and an anthracycline, such as idarubicin (Idamycin®). Nevertheless, some setbacks can occur, such as:
- hemorrhage (heavy bleeding) during the treatment's initial phases
- resistance to treatment
- the return of APL (relapse)
Patients in remission must get long-term follow-up care to determine whether they are cured or need further therapy.
The ideal duration of maintenance therapy is also being investigated. Currently, it consists of 2 years of 6-mercaptopurine (6-MP), methotrexate, and ATRA.
The drug arsenic trioxide (ATO) (Trisenox®) is sometimes given to APL patients if:
- their leukemia has returned
- their leukemia can't be controlled with chemotherapy and ATRA
- they've developed persistent minimal residual disease (MRD - when a low level of remaining APL cells can't be detected by standard tests) - after postremission therapy
Patients who do not have a donor, or cannot have an allogeneic stem cell transplant for other reasons, may be candidates for an autologous stem cell transplantation. Arsenic trioxide is approved to treat APL patients who have relapsed or are resistant to treatment with chemotherapy and ATRA.
If you would like to read about these drugs individually, including information about side effects, click here.
Clinical Trials for APL
Clinical trials are under way to study the use of ATRA with other classes of drugs.