What is acute promyelocytic leukemia?

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

Bleeding associated with APL can appear as body bruising, pinhead-sized rashes under the skin, nosebleeds, bleeding in the mouth, and blood in the urine. Affected women may also experience excessive blood flow as part of menstrual bleeding. Fever, fatigue, increased susceptibility to infection, and bone and joint pain are some of the other main symptoms of APL.

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

The prognosis of acute promyelocytic leukemia is carried out based on several factors, including the white blood cell (WBC) count. APL is a subtype of acute myeloid leukemia (AML), which is classified into seven main subtypes, M1 through M7, based on the type of myeloid cell that is abnormal. Of these seven subtypes, patients with M3 or acute promyelocytic leukemia have the best chance of survival and better outcomes. APL is most often seen in middle-aged people and young children of Latin American or Mediterranean descent.

The treatment method for APL is different from that of other leukemia subtypes. A special form of "differentiation therapy" called all-trans retinoic acid (ATRA) therapy is used to treat APL. ATRA induces immature promyelocytes to mature and thus prevents their proliferation. ATRA followed by chemotherapy was 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.

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