About 600 to 800 people develop acute promyelocytic leukemia (APL) in the United States each year.

Leukemia is a group of cancers that develop in the cells that produce blood cells. It is classified as acute leukemia if it progresses quickly without treatment.

APL is a subtype of an acute form of leukemia called acute myeloid leukemia (AML). It’s one of the eight subdivisions of AML and is characterized by an increase in immature white blood cells called promyelocytes.

Read on to learn about how APL differs from other leukemias, how to spot signs and symptoms, the diagnostic process, and how it’s treated.

APL is one of the many types of leukemia. It is a relatively rare type of AML, as it only makes up about 7 to 8 percent of adult AML cases. It’s one of the eight subdivisions of AML and is characterized by an increase in immature white blood cells called promyelocytes.

APL starts with a mutation in the DNA of blood-producing cells in your bone marrow. Specifically, it’s caused by mutations on chromones 15 and 17, which leads to the creation of an abnormal gene called PML/RARa.

These gene mutations lead to the overproduction of immature promyelocytes. Because there are so many promyelocytes, there aren’t enough of the normal red blood cells, white blood cells, and platelets that your body needs. This can lead to potentially life threatening complications such as bleeding and poor blood clotting.

Before the development of modern medical treatments, APL had one of the poorest prognoses of all acute leukemias, and people usually died within a month. Now, nearly 100 percent of people with APL go into remission, which is when cancer is no longer detectable in your body.

The symptoms of APL tend to be nonspecific and can resemble those of many other conditions or other types of leukemia. They can include:

When to see a doctor

The development of APL is a medical emergency, and prompt treatment is needed. Early warning signs can be difficult to recognize since they’re not specific to this disease.

You should consult a medical professional if you have any potential warning symptoms of APL, even if leukemia is unlikely to be the cause. Some particular symptoms to look out for include:

  • unexplained fever
  • chronic fatigue
  • pale complexion
  • unusual bleeding
  • frequent infections
  • bruising more easily than usual
  • bone or joint pain
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About half of people diagnosed with APL are under age 40. The average age of diagnosis is 44 years old.

An APL diagnosis is made based on the results of certain lab tests, together with a physical exam and your medical history.

Blood tests

If your doctor suspects that you have APL, they’ll likely perform a complete blood count test to check the levels of your blood cells. People with APL usually have low levels of:

Cells in the blood sample can also be checked for abnormalities by a hematologist, a doctor who specializes in the blood.

Bone marrow tests

If blood tests reveal evidence of leukemia, your doctor will likely want to take a bone marrow biopsy. This test involves taking a small amount of the spongy marrow inside of your bones to study. The hip bone is often used.

Before the procedure, you’ll be given a local anesthetic, so you won’t feel pain. The biopsy will be taken with a long needle.

Lab tests

A number of lab tests may be used to analyze bone marrow cells, including:

  • Flow cytometry. Bone marrow cells are suspended in fluid and flow through a laser so health professionals can identify abnormalities in cells.
  • Karyotyping. Cells are stained and examined under a microscope while they’re dividing.
  • Fluorescence in situ hybridization. Certain areas on your cells’ chromosomes are stained to identify large genetic changes.
  • Polymerase chain reaction. Health professionals perform a DNA sequencing technique that allows them to identify mutations and small genetic changes.
  • Next generation sequencing. This is a technique that allows researchers to evaluate mutations in multiple genes at the same time.

Most people with APL are treated with a drug called all-trans-retinoic acid (ATRA) in combination with arsenic trioxide. These medications are often enough to put APL into remission.

Additional cycles of ATRA with arsenic trioxide are usually administered after the cancer is in remission to keep it undetectable.

People who have a high risk of the disease returning may be given chemotherapy drugs. These chemotherapy drugs are often administered directly into your cerebral spinal fluid. People with a low risk of the disease returning likely won’t be given chemotherapy.

Some patients may also have to undergo maintenance therapy, which usually consists of ATRA or ATRA and chemotherapy. Maintenance therapy is usually given for about a year.

Getting quick treatment for APL is critical for increasing your chances of a good outcome. Studies report a 2-year survival rate as high as 97 percent in patients receiving ATRA treatment.

On the other hand, the outlook for people with APL who don’t receive treatment is very poor. Half of this group may live less than a month after diagnosis due to complications like infections and bleeding.

APL is a relatively rare type of leukemia that causes a buildup of immature white blood cells in your blood and bone marrow. It’s caused by genetic changes in the cells that create blood cells.

APL used to have one of the poorest prognoses of any acute leukemia, but thanks to advances in medical research, it now has one of the highest survival rates.

It can be difficult to recognize APL since many of its symptoms aren’t specific to this disease. It’s a good idea to check with a healthcare professional if you notice any potential warning signs such as abnormal bleeding, bruising easier than usual, or unexplained fatigue.