TIF1/TRIM24::FGFR1-rearranged myeloid/lymphoid neoplasm with eosinophilia and tyrosine kinase gene fusion presenting as mixed-phenotype acute leukemia: a case report.

Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions are rare aggressive malignancies. FGFR1-rearranged cases are particularly high-risk. Among FGFR1 fusion partners, TIF1/TRIM24::FGFR1 is exceptionally rare. We report a 33-year-old woman presenting with fever, skin bruising, leukocytosis, thrombocytopenia, and circulating blasts. Bone marrow and flow cytometry identified abnormal B-lymphoblasts, myeloid blasts, and monocytic populations, supporting a mixed-phenotype acute leukemia presentation. Cytogenetics detected t(8;7)(p11;q34) translocation. Whole-transcriptome sequencing identified a TIF1/TRIM24::FGFR1 fusion transcript, confirmed by Sanger sequencing and FISH. RUNX1 missense mutation was also detected. The patient achieved complete remission after induction chemotherapy. However, after discontinuation of therapy and refusal of allo-HSCT, she relapsed rapidly with clonal evolution. A second remission was transient, and the patient died of cerebral hemorrhage. This case highlights the aggressive biology of TIF1/TRIM24::FGFR1-rearranged MLN-TK, the limitation of conventional chemotherapy, and the potential value of fusion-specific monitoring. Early allo-HSCT should be considered once remission is achieved, and FGFR1-directed therapy may represent a potential option in selected patients. However, clinical evidence remains limited and further studies are required.