Acute Promyelocytic Leukemia (APL) Overview

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Updated on June 21, 2022

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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 the United States, APL accounts for about 10-15% of all AML cases.

Doctor consoling a woman in her doctor's office — megaflopp / iStockphoto

While it is similar in many ways to the other subtypes, APL is distinctive and has a specific treatment regime. Treatment outcomes for APL are very good, and it is considered the most curable type of leukemia, with cure rates as high as 90%.

Genetics and Acute Promyelocytic Leukemia (APL)

The genetic abnormality 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 young and immature.

What Are Promyelocytes?

Promyelocytes are intermediate cells in the white blood cell maturation process, with the "babies" being myeloblasts or blasts, and the adults being the myelocytes known as neutrophils, eosinophils, basophils, and monocytes.

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

People with APL have 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
Delayed healing from cuts and bruises
Achy bones or joints
Difficulty fighting off infections

In addition to these signs of AML, people with APL also have other characteristic symptoms.

They will often have:

Severe bleeding problems such as bruising, nosebleeds, blood in the urine or bowel movements
Abnormal, excessive clotting of the blood

Girls and women with APL may notice unusually heavy menstrual periods.

The symptoms of leukemia can be vague, and may also occur with 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

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

Most people with APL are treated initially with a combination of all-trans retinoic acid (ATRA), a specialized form of vitamin A and with arsenic trioxide (ATO). ATRA therapy is unique in that it 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). This phase of treatment is referred to as "induction."

For many people, the combination of ATRA and ATO is curative. For some people, chemotherapy treatment is used as well.

After initial treatment, ATRA is often continued for at least a year, sometimes combined with other medications. This last phase of treatment is called "maintenance."

Prognosis

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

Coping and Support

Even though APL has an excellent prognosis, the diagnosis and treatment process can be exhausting for you. Make sure you give yourself time to rest. Consider reaching out to family and friends—and accept their help.

Take time to learn about survivorship and coping. When cancer treatment ends, instead of elation, many people feel depressed. Persistent side effects of treatment and time spent on the emotional roller coaster of cancer can leave you wondering if you will ever feel normal again. There are resources to help cancer survivors thrive. Studies actually tell us that cancer changes people in good ways, not just bad.

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