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What Is Acute Promyelocytic Leukemia (APL)?

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Updated October 27, 2010

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Acute promyelocytic leukemia (APL) is a subtype of acute myelogenous leukemia (AML), a cancer of the blood. You may also hear it referred to as M3 AML.

In North America, APL accounts for about 10% of all AML cases. In Italy and areas of South America, APL may represent as many as 65% of cases.

While it is similar in many ways to the other subtypes, it distinctive and has a very specific treatment regime.

Treatment outcomes for APL are very good, and it is considered the most curable type of leukemia. Cure rates are as high as 90%.

The genetic abnormality or mutation most often seen in the DNA of the leukemia cells is a translocation between chromosomes 15 and 17. This means that a part of chromosome 15 breaks off, and is exchanged with a part of chromosome 17. This mutation leads to the production of a protein that causes blood cell development to get “stuck” at the promyelocytic stage, when white blood cells are very young and immature.

Promyelocytic leukemia cells can be compared to human teenagers. They look a bit like adults, but they can’t get jobs, pay the bills, drive a car, or do the daily functions of fully mature humans. Likewise, promyelocytic blood cells are too underdeveloped to perform the roles of fully mature white blood cells in the body.

Signs and Symptoms of APL

Patients with APL exhibit many of the same symptoms as other types of AML. Most of the signs of leukemia are the result of cancer cells “crowding out” the bone marrow and interfering with the production of normal, healthy red blood cells, white blood cells and platelets. These signs and symptoms include:

  • Having low energy, or feeling tired all the time
  • Feeling short of breath when doing regular activities
  • Pale skin
  • Unexplained fevers
  • Increased healing time of cuts and bruises
  • Achy bones or joints
  • Difficulty “fighting off” infections

In addition to these signs of AML, APL patients also show other characteristic symptoms. They will often have severe bleeding problems such as bruising, nosebleeds, blood in the urine or bowel movements. Girls and women with APL may notice unusually heavy menstrual periods.

At the same time, APL may also cause the blood to have abnormal, excessive clotting.

The symptoms of leukemia can be very vague, and may also be signs of other, non-cancerous conditions. If you are concerned about your health, or the health of a loved one, it is always best to seek the advice of a medical professional.

Treatment of APL

APL treatment is very different than that of other types of acute leukemia, so properly identifying it is critical.

Most APL patients are treated initially with all-trans retinoic acid (ATRA), a specialized form of vitamin A. ATRA therapy is unique in that it actually forces the promyelocytic leukemia cells to mature, a bit like how graduating college forces the teenagers in our comparison into the adult role (well, at least sometimes).

While ATRA can get an APL patient into remission by pushing all the leukemia cells into maturity, it cannot cure the source of the leukemia. As a result, long-term outcomes for treatment improve when physicians add some standard chemotherapy.

If the leukemia does not respond to ATRA and chemotherapy, or if it returns, APL can also be treated with arsenic trioxide (ATO).

Treatment of APL is successful in the vast majority of cases.

Sources

Jurcic, J., Soignet, S., Maslak, P. Diagnosis and Treatment of Acute Promyelocytic Leukemia. Current Oncology Reports 2007. 9: 337-344.

Lemons, R., Keller, S., Gietzen, D., Dufner, J, Rebentisch, M.,Feusner, J., Eilender, D. Acute Promyelocytic Leukemia Journal of Pediatric Hematology/ Oncology 1995. 17:198- 210.

Sanz, M. Treatment of Acute Promyelocytic Leukemia. American Society of Hematology 2006. 147- 155.

Wiernik, P., Gallagher, R., Tallman, M. "Acute Promyelocytic Leukemia" in Wiernik, P., Goldman, J., Dutcher, J., Kyle, R. (eds.)(2003) Neoplastic Diseases of the Blood- 4th ed. New York: Cambridge University Press.

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