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Acute megakaryoblastic leukemia with myeloid sarcoma among a pediatric patient harbouring RBM15::MRTFA: a case report and literature review

Year: 2026

Type: article

Abstract: BACKGROUND: Acute megakaryoblastic leukemia (AMKL) is a rare subtype of acute myeloid leukemia (AML) that predominantly affects young children. The RBM15::MRTFA fusion gene is a recurrent genetic alteration in pediatric non-Down syndrome associated AMKL (n-DS-AMKL). Myeloid sarcoma (MS), an extramedullary solid tumor of immature myeloid cells, can be a presenting feature of AML and poses significant diagnostic challenges, often leading to initial misdiagnosis. CASE PRESENTATION: We report the case of a 2-year-old boy who initially presented with a right frontal cranial mass. Imaging and initial histopathology were suggestive of Langerhans cell histiocytosis (LCH). Following surgical resection, the tumor recurred within four months. A subsequent biopsy of the intracranial lesion, prompted by the patient's deteriorating condition, revealed a malignant small round blue cell tumor. Immunohistochemistry was initially inconclusive, leading to a provisional diagnosis of a poorly differentiated vascular tumor. However, next-generation sequencing (NGS) analysis of the biopsy specimen identified the RBM15::MRTFA fusion gene, confirming the diagnosis of AMKL with MS. Bone marrow examination subsequently confirmed the leukemic involvement. The patient achieved complete remission after induction chemotherapy according to the SCCCG-AML 2020 protocol, followed by successful umbilical cord blood hematopoietic stem cell transplantation (HSCT). At the last follow-up, the patient remained in complete remission with no significant graft-versus-host disease (GVHD). CONCLUSIONS: This case highlights the critical role of comprehensive molecular profiling, particularly NGS, in the accurate diagnosis of AMKL presenting as myeloid sarcoma, especially when initial pathological findings are ambiguous. RBM15::MRTFA-positive AMKL can present with isolated extramedullary disease, and a high index of suspicion is necessary to avoid misdiagnosis. Early and precise genetic diagnosis is essential for guiding appropriate, potentially curative therapy, including HSCT, in pediatric patients.

Source: BMC Pediatrics

DOI: 10.1186/s12887-026-06656-2