Novel <em>EVI5</em>::<em>BRAF </em>Gene Fusion in Infantile Fibrosarcoma: A Case Report and Review of Literature

Introduction: Infantile fibrosarcoma is a malignant tumor of fibroblastic origin, typical in early childhood, locally aggressive, and characterized by molecular alterations that activate tyrosine kinase signaling, primarily the ETV6::NTRK3 fusion. In recent years, a series of fusions different from the classic one have been described, including NTRK1, RAF1, and BRAF. In this paper, we present a case of IFS with a novel EVI5::BRAF fusion. Methods: We received a humeral surgical resection specimen. After macroscopic carving, tumor samples were collected, processed, and stained with hematoxylin-eosin. Various immunohistochemical and molecular techniques were applied to sections of the non-decalcified tumor. Results: We observed a spindle cell neoplasm growing in intertwined fascicles within a fibrous stroma, without the formation of immature osteoid matrix. Weak and focal immunoreactivity for S100 was observed. SATB2 exhibited diffuse and intense staining, with focal expression of osteonectin and negativity for caldesmon, smooth muscle actin, desmin, GFAP, SOX10, MelanA, panTRK, and HMB45. The Ki67 index was 7%, and the tumor harbored an EVI5::BRAF genetic fusion. Conclusions: To the best of our knowledge, the EVI5::BRAF fusion has not yet been described in BRAF fusions in IFS. Nevertheless, further studies are needed to define the prognostic features of these emerging BRAF sarcomas.