A 10-year-old boy arrived with two weeks of progressive fatigue, low-grade fever, intermittent gum bleeding, easy bruising, and reduced activity. He looked pale and had scattered ecchymoses, but doctors found no significant lymphadenopathy or hepatosplenomegaly. Laboratory testing revealed pancytopenia: hemoglobin of 7.8 g/dL, a leukocyte count of 2.1 × 10⁹/L, and a platelet count of 32 × 10⁹/L.

Under the microscope, the smear showed abnormal promyelocytes with hypergranular cytoplasm and occasional Auer rods—needle-shaped azurophilic cytoplasmic inclusions that are classic features of acute promyelocytic leukemia (APL). One cell captured in the case report’s figure was a so-called faggot cell, a hypergranular promyelocyte packed with numerous bundled Auer rods, a morphologic hallmark of the disease. Coagulation studies showed a prolonged prothrombin time (19.8 seconds, INR 1.8), an activated partial thromboplastin time of 46.2 seconds, D-dimer above 20.0 μg/mL FEU, and hypofibrinogenemia with fibrinogen at 0.9 g/L. Together, these findings were consistent with disseminated intravascular coagulation.

In a child presenting with cytopenias and a bleeding diathesis, the differential diagnosis is broad. Acute lymphoblastic leukemia, other acute myeloid leukemia subtypes, aplastic anemia, and severe infection with disseminated intravascular coagulation all belong on the list. But the combination of hypergranular promyelocytes, Auer rods, and coagulopathy strongly suggested APL.

Bone marrow examination confirmed a predominance of abnormal promyelocytes, and flow cytometry demonstrated an immunophenotype consistent with APL: expression of CD13, CD33, and myeloperoxidase, with absent CD34 and HLA-DR expression. Conventional cytogenetic analysis then identified the t(15;17)(q24;q21) translocation, fluorescence in situ hybridization confirmed the PML-RARA rearrangement, and reverse transcription polymerase chain reaction detected the PML-RARA fusion transcript. With those results, the diagnosis of APL was formally established.

The management decisions in this case followed the approach described in the report. All-trans retinoic acid (ATRA) was initiated upon clinical suspicion, before cytogenetic confirmation, because of the high risk of early hemorrhagic complications. The child also received aggressive supportive transfusion therapy to maintain platelet counts and fibrinogen levels. According to the report, early mortality in APL is primarily attributable to hemorrhage secondary to consumptive coagulopathy, so ATRA should be initiated as soon as APL is clinically suspected, without awaiting confirmatory testing. The report states that recognition of hypergranular promyelocytes with multiple Auer rods remains essential for early therapeutic decision-making.

After diagnostic confirmation, the patient received induction therapy with ATRA plus arsenic trioxide, without additional chemotherapy, consistent with the management of low-risk APL. The response was rapid. Clinically and hematologically, the child improved quickly, with resolution of bleeding manifestations and normalization of coagulation parameters. Complete molecular remission, confirmed by negative RT-PCR for the PML-RARA fusion transcript, was documented after completion of induction therapy. Notably, no evidence of differentiation syndrome emerged during treatment in this case.

The case also underscores why morphology still matters in an era of molecular diagnostics. FISH, cytogenetics, and RT-PCR provide definitive confirmation of the PML-RARA rearrangement, but those results take time, and a child with a fibrinogen of 0.9 g/L and gum bleeding cannot wait for them. The smear findings—hypergranular cytoplasm, Auer rods, faggot cells—paired with the coagulation profile gave the treating team enough evidence to start ATRA immediately, a decision the report credits with helping to prevent fatal hemorrhagic complications. Definitive diagnosis, in the authors’ framework, rests on demonstrating the PML-RARA rearrangement using cytogenetic and molecular techniques, but the therapeutic clock starts at the microscope.

For clinicians evaluating children with cytopenias and bleeding, the message is concrete: when a peripheral smear shows hypergranular promyelocytes with Auer rods and coagulation studies show disseminated intravascular coagulation, APL belongs at the top of the differential, and ATRA should not be delayed. This single case, reported with full morphologic, immunophenotypic, cytogenetic, and molecular documentation, adds a pediatric example to the literature supporting that approach, and its outcome—rapid hematologic recovery, molecular remission after induction, and no differentiation syndrome—illustrates the clinical benefit of early diagnosis and targeted differentiation therapy in children.

Subject of Research: A pediatric case report describing the clinical and morphologic features of acute promyelocytic leukemia with PML-RARA rearrangement.

Article Title: Acute Promyelocytic Leukemia With PML‐RARA Rearrangement: Clinical and Morphologic Features

Article References: Elendu, C., Johnson, A. D., & Debua, A. T. (2026). Acute Promyelocytic Leukemia With PML‐RARA Rearrangement: Clinical and Morphologic Features. Clinical Case Reports, 14(11), Article e73830. https://doi.org/10.1002/ccr3.73830

Image Credits: AI Generated

DOI: 10.1002/ccr3.73830

Keywords: acute promyelocytic leukemia, PML-RARA, Auer rods, faggot cells, disseminated intravascular coagulation, all-trans retinoic acid, arsenic trioxide, pediatric oncology, flow cytometry, cytogenetics, molecular remission, hematology