Myeloid/lymphoid neoplasm with eosinophilia and fibroblast growth factor receptor 1 rearrangement presenting as T-lymphoblastic lymphoma: A rare diagnostic challenge

Myeloid/lymphoid neoplasm with eosinophilia and fibroblast growth factor receptor 1 (FGFR1) rearrangement, formerly known as 8p11 myeloproliferative syndrome or stem cell leukemia/lymphoma syndrome, is an exceptionally rare hematologic malignancy characterized by a Breakpoint Cluster Region::Abelson Murine Leukemia Viral Oncogene Homolog 1 (BCR::ABL1)-negative myeloid neoplasm, eosinophilia, and frequent association with aggressive lymphoid neoplasms, most commonly T-lymphoblastic lymphoma (T-LBL). We report the case of a 22-year-old man who presented with fever, generalized lymphadenopathy, and hepatosplenomegaly, initially raising a clinical suspicion of lymphoma. Hematological evaluation, including complete blood count, peripheral blood smear, and bone marrow examination, demonstrated features of a chronic myeloproliferative neoplasm with eosinophilia, closely resembling chronic myeloid leukemia. Histopathological examination of the lymph node revealed T-LBL. Molecular analysis was negative for BCR::ABL1 transcripts, while conventional cytogenetic analysis identified t(8;13) (p11.2;q12). Fluorescence in situ hybridization confirmed FGFR1 rearrangement, establishing the diagnosis of myeloid/lymphoid neoplasm with eosinophilia and FGFR1 rearrangement. This case highlights the diagnostic challenge posed by this rare entity because of its overlapping clinical and hematological features with lymphoma and chronic myeloproliferative neoplasms. Early recognition through cytogenetic and molecular testing is essential for timely diagnosis and appropriate management. Allogeneic hematopoietic stem cell transplantation remains the only established potentially curative treatment, although emerging FGFR1-targeted therapies may provide additional therapeutic options in the future.