Acute promyelocytic leukemia, often referred to as APL, is a type of cancer that affects the production of blood cells. It is characterized by a shortage of mature myeloid blood cells and an overabundance of immature cells known as promyelocytes. This condition arises from a genetic abnormality, where material is exchanged between chromosomes 15 and 17, denoted as t(15;17). This translocation is not just associated with APL; it is the underlying cause.APL was first identified as a unique disease in 1957 and represents 5-10% of acute myeloid leukemia (AML) cases. It predominantly affects young adults and is categorized as the M3 variant of AML according to the French-American-British (FAB) Classification.The symptoms of APL are varied and include tiredness, minor infections, and a tendency to bleed, among others. Patients often show low levels of red blood cells, certain white blood cells like granulocytes and monocytes, and platelets, which are crucial for normal blood clotting. Consequently, blood transfusions may be necessary for those with APL.This leukemia is frequently linked with a condition similar to disseminated intravascular coagulation (DIC), leading to a significant bleeding tendency. This bleeding can appear as small spots under the skin, bruises, nosebleeds, mouth bleeding, and excessive menstrual bleeding in menstruating females. These symptoms might precede a leukemia diagnosis by several weeks.The t(15;17) translocation in APL results from breaks in chromosomes 15 and 17. The break in chromosome 15 affects the promyelocytic leukemia (PML) gene, which normally suppresses cell growth, while the break in chromosome 17 impacts the retinoic acid receptor alpha (RARa) gene, which controls myeloid cell differentiation. This translocation creates a PML/RARa fusion gene, leading to an accumulation of promyelocytes by halting their maturation.Treatment for APL is distinct from other AML types, primarily involving all-trans retinoic acid (ATRA), a form of differentiation therapy. ATRA promotes the maturation of promyelocytes by activating the RAR receptor, thereby reducing their proliferation. While ATRA can induce complete remission in most APL patients, it does not eliminate the leukemic cells, necessitating its use with chemotherapy drugs such as anthracycline for better outcomes. This combination treatment improves survival rates compared to chemotherapy alone and reduces relapse rates. Maintenance therapy with ATRA and possibly low-dose chemotherapy further decreases relapse chances.The prognosis for APL depends on factors like the white blood cell count at diagnosis. Currently, more than 90% of newly diagnosed APL patients achieve complete remission, and approximately 75% are cured with ATRA and chemotherapy. For those who relapse, treatments may include arsenic trioxide.ATRA therapy has transformed APL treatment and significantly enhanced patient outcomes. ATRA syndrome, a potential side effect, can cause fever, respiratory issues, and fluid retention, but it can be prevented with chemotherapy or dexamethasone if the white blood cell count rises.In summary, APL is a type of acute myeloid leukemia caused by the t(15;17) chromosome translocation. It is characterized by a distinct cellular appearance classified as M3 in the FAB Classification and responds well to treatments involving retinoids, chemotherapy, and arsenicals.
