What is Acute Promyelocytic Leukemia?

Acute promyelocytic leukemia (APL), or acute myeloid leukemia subtype M3, is a type of cancer affecting the blood and bone marrow. This condition, which is characterized by severe bleeding disorders, results from the accumulation of immature white blood cells called "promyelocytes" in the blood and bone marrow. The promyelocytes replace the normal blood cells and platelets, and causes a drop in the normal blood cell count.

The bleeding associated with acute promyelocytic lukemia may appear as body bruising, pinhead-sized eruptions under the skin, nosebleeds, bleeding in the mouth, and blood in the urine. Afflicted women also may experience excessive blood flow as part of menstrual bleeding. Fever, fatigue, increased susceptibility to infections, and bone and joint pain are some of the other major symptoms of APL.

The increased susceptibility to fever and infections is brought about by the lowering of the body’s defenses due to the reduction of the mature white blood cells. Similarly, the constant bleeding and the rapid decrease in red blood cells and platelets leads to anemia and fatigue. The bleeding symptoms of acute promyelocytic leukemia is sometimes found associated with disseminated intravascular coagulation (DIC), where bleeding occurs from the skin, respiratory and digestive tracts, and even the surgical wounds on the body.

An acute promyelocytic leukemia prognosis is carried out based on several factors, including a white blood cell (WBC) count. APL is a subtype of acute myeloid leukemia (AML), which is classified into seven major subtypes, M1 to M7, depending on the type of myeloid cell which is abnormal. Of these seven subtypes, the patients with M3 or acute promyelocytic leukemia are found to have higher chances of survival and better outcomes. APL is most commonly observed in middle-aged people and in young children of Latin American or Mediterranean ancestry.

The method of treatment for APL is different from that of other leukemia subtypes. A special form of "differentiation therapy," called all-trans-retinoic-acid (ATRA) therapy, is employed for the treatment for acute promyelocytic leukemia. ATRA induces the immature promyelocytes to mature, and thus prevents their proliferation. ATRA followed by chemotherapy is found to cure APL completely in more than 75% of patients. Some patients may experience a relapse of APL; however, maintenance treatment with ATRA, low-dose chemotherapy, and arsenic trioxide has been found to reduce relapses of this disease.