Diagnostic workup of a suspected patient with APL should include a case history and physical examination with focus on bleeding tendencies, recurrent infections and anemic symptoms such as fatigue or pallor. A complete blood count with a differential should be performed. During a peripheral blood smear the technologist should be looking for abnormal promyelocytes with abundant azurophilic granulation and multiple auer rods. A bone marrow aspirate with cytology, cytochemistry, immunophenotyping, FISH, RT-PCR, and cytogenetics should be included. Diagnostic coagulation tests such as PT, aPTT, fibrinogen, and a D-dimer should be performed. During the immunophenotyping the characteristic phenotype of APL is CD33, CD13, CD45, CD64, and CD117 positive. Also APL is HLA-Dr negative which differentiates it from other AMLs which are HLA-Dr positive.
Early initiation of induction therapy ATRA before confirmation of diagnosis has changed the management of APL. APL is curable due to the initiation of ATRA. APL is considered a severe hematologic emergency due to its rapidly progressing bleeding diathesis and risk of intracerebral hemorrhage. Making a presumptive diagnosis based on the peripheral blood smear and bone marrow aspirate along with the patient history is important because the earlier that the patient begins therapy the better the outcome. ATRA and blood product support should be started as early as possible. APL blasts are highly sensitive to anthracyclines. Anthracycline chemotherapy with combination ATRA boasts remission rates of more than 90%. ATRA otherwise known as all-trans retinoic acid is a derivative of retinoic acid which reverses the differentiation block of APL blasts. Arsenic therapy with arsenic trioxide is approved in Europe and the United States for relapsed and refractory APL.
Aggressive supportive therapy involves FFP, cryoprecipitate and platelets to maintain platelet levels greater than 30,000-50,000/uL and fibrinogen levels above 150 mg/dL. This regimen typically lasts during the first week of induction therapy while the coagulation disorder resolves.
There are significant adverse effects with therapy for APL. A common complication during induction therapy with ATRA or ATO (arsenic) is the development of hyperleukocytosis. APL differentiation syndrome is a life-threatening complication that develops a fever, edema/weight gain, respiratory distress, lung infiltrates, and pleural or pericardial effusions. Differentiation syndrome typically occurs within the first two weeks of the onset of therapy. Intravenous Dexamethasone is recommended immediately in the suspicion of APL differentiation syndrome. In mild cases of differentiation syndrome, ATRA or ATO therapy can just be interrupted and continued after symptoms regressed and when leukocyte counts decrease. Arsenic trioxide toxicity causes electrolyte shifts, particularly involving potassium and magnesium which to no surprise can alter ECG readings causing most commonly a QT interval prolongation. ATO therapy must be discontinued in severe prolongations due to the increased risk of cardiac arrhythmias. Documented chemotherapy adverse effects include the typical nausea and vomiting, increased infections, anemia, thrombocytopenia, increased bleeding tendencies which is exacerbated due to the coagulopathy associated with APL, and cardiac effects. With long-term chemotherapy there is an increased risk of drug-induced secondary malignancies.
Choice of treatment and timing of treatment is extremely important. As mentioned earlier it is very important to start induction therapy upon the first suspicion of APL, even before molecular confirmation occurs.