Myeloid/lymphoid neoplasm with FLT3 gene fusion: report of a case with a novel t(5;13)(q13;q12) SSBP2::FLT3 fusion.

Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions (M/LN-eo-TK) are diverse, with most cases showing a combination of lymphoblastic leukemia/lymphoma and myeloproliferative features. Various tyrosine kinase fusion genes have been identified, including FLT3 fusions. RNA based next generation sequencing studies offer an effective approach to detect such pathogenic fusion genes, including the novel SSBP2::FLT3 fusion described here. Timely identification of this fusion gene led to targeted management of our patient, who achieved complete resolution of his FDG-avid lymphadenopathy only after the addition of gilteritinib. Two years after successful bone marrow transplant, the patient remains in complete remission. Clinicians and pathologists should have a low index of suspicion for a M/LN-eo-TK when evaluating patients with and without unexplained eosinophilia in the context of extramedullary lymphoid or myeloid disease or unusual myeloproliferative disorders.