What Is Acute Promyelocytic Leukemia (APL)?

What does it mean if you have acute promyelocytic leukemia (APL) and how is it treated?

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.  It occurs equally in women and men, and the median age of onset is age 40.

While it is similar in many ways to the other subtypes, APL is 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%.

Genetics and Acute Promyelocytic Leukemia (APL)

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.

What Are Promyelocytes?

Promyelocytes are cells that fall in line in the development of these type of white blood cells, 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.

Patients with APL exhibit many of the same symptoms as other types of acute myelogenous leukemia (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, there is often abnormal, excessive clotting of the blood.

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.

The treatment of acute promyelocytic leukemia (APL) 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). This phase of treatment is referred to as "induction."

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.  This face of treatment is referred to as "consolidation."

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

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.

Even though acute promyelocytic leukemia has an excellent prognosis, at least with respect to leukemia, "getting there" can be difficult and draining.  Reach out to family and friends.  Don't worry about needing help and receiving help at this stage in your life.  You may be surprised how it not only helps you, when others help, but brings happiness to them as well.  Check out these tips on coping with leukemia and lymphoma.

Take time to learn about survivorship.  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.  Ask for help, and don't just accept your "new normal."  There is much that can be done to help cancer survivors thrive.  And don't forget that, at times, good can come from cancer as well.  Studies actually tell us that cancer changes people in good ways, not just bad.