Background: Juvenile myelomonocytic leukemia (JMML) is a rare and aggressive pediatric hematologic malignancy characterized by clonal proliferation of myelomonocytic cells. It predominantly affects young children and presents significant diagnostic challenges due to overlapping features with other myeloid disorders. Here, we report the case of a 2-year-old male patient with unique genetic findings involving the NPM::MLF1 fusion gene and NRAS mutation.

Methods: A comprehensive diagnostic evaluation was conducted, including physical examination, complete blood count, bone marrow aspiration, flow cytometry, cytogenetic analysis, and molecular testing for fusion genes. Imaging studies, including abdominal ultrasound, were also performed. Therapeutic interventions included hydroxyurea for leukocytosis and supportive transfusions. Family members declined chemotherapy and hematopoi-etic stem cell transplantation.

Results: The patient presented with leukocytosis, anemia, thrombocytopenia, splenomegaly, and abnormal bone marrow findings consistent with JMML. Genetic testing revealed a rare t(3;5)(q25;q34) involving the NPM:: MLF1 fusion gene and an NRAS mutation. Supportive treatment was provided, but the family declined definitive chemotherapy and hematopoietic stem cell transplantation.

Conclusions: This case represents a rare presentation of JMML with t(3;5)(q25;q34) involving the NPM::MLF1 fusion gene, a finding uncommon in pediatric myeloid malignancies. The presence of this genetic abnormality presents significant diagnostic and therapeutic challenges, emphasizing the need for comprehensive genetic profiling in JMML. The rarity of the NPM::MLF1 fusion complicates the establishment of a standard treatment proto-col, underscoring the necessity for individualized treatment approaches and further research.