Myeloid sarcoma with RBM15::MRTFA (MKL1) mimicking vascular neoplasm

Area of Science:

• Hematology
• Pediatric Oncology
• Molecular Diagnostics

Background:

• Extramedullary involvement in acute myeloid leukemia (AML) is uncommon, particularly in acute megakaryoblastic leukemia.
• Myeloid sarcoma, a form of extramedullary AML, can present as solid tumors and may be misdiagnosed as non-hematologic malignancies.
• The RBM15::MRTFA(MKL1) fusion is a rare genetic abnormality associated with AML.

Purpose of the Study:

• To report a rare case of acute megakaryoblastic leukemia presenting as extramedullary myeloid sarcoma in an infant.
• To highlight the diagnostic challenges and potential misdiagnosis of non-hematologic malignancies.
• To emphasize the significance of molecular diagnostics, specifically RBM15::MRTFA(MKL1) fusion, in accurate AML classification.

Main Methods:

• Clinical presentation of a 7-month-old infant with leukocytosis, hepatosplenomegaly, lymphadenopathies, and a thigh mass.
• Initial biopsy of the thigh lesion misinterpreted as a malignant vascular tumor.
• Subsequent bone marrow biopsies and RNA sequencing of soft tissue for genetic analysis.

Main Results:

• The patient presented with symptoms suggestive of a solid tumor, leading to an initial misdiagnosis.
• Bone marrow examination revealed hypercellularity with specific blast morphology and immunophenotype (CD34+, CD61+).
• RNA sequencing confirmed the presence of the RBM15::MRTFA(MKL1) fusion in the soft tissue biopsy, establishing the AML diagnosis.

Conclusions:

• Acute myeloid leukemia with RBM15::MRTFA(MKL1) fusion can manifest primarily as extramedullary lesions (myeloid sarcoma).
• This presentation can lead to diagnostic delays and misdiagnosis as non-hematologic malignancies.
• Early consideration of AML and comprehensive molecular testing are crucial for accurate diagnosis and appropriate treatment in pediatric cases with extramedullary masses.