The EWSR1 antibody is a crucial tool in diagnostic pathology and cancer research, targeting the Ewing sarcoma breakpoint region 1 (EWSR1) protein encoded by the *EWSR1* gene on chromosome 22. This gene is frequently involved in chromosomal translocations associated with various soft tissue and bone tumors, most notably Ewing sarcoma, where *EWSR1* fuses with *FLI1* or other ETS-family transcription factors. EWSR1. a member of the TET family of RNA-binding proteins, plays roles in transcriptional regulation, RNA splicing, and chromatin remodeling. The antibody is primarily used to detect EWSR1 rearrangements or aberrant protein expression in tumors via immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), or molecular assays. Its diagnostic utility extends to distinguishing Ewing-like sarcomas from histologic mimics and identifying other EWSR1-rearranged tumors, such as clear cell sarcoma, myxoid liposarcoma, and angiomatoid fibrous histiocytoma. However, cross-reactivity with normal tissues or other fusion partners necessitates careful interpretation. In research, EWSR1 antibodies help elucidate the oncogenic mechanisms of fusion proteins and explore therapeutic targets. Commercial clones vary in specificity, with common options (e.g., clone G5) validated for both IHC and Western blotting.