Ewing’s Sarcoma of the Prostate Presenting as Back Pain: A Report of a Rare Case and Review of the Literature

Ewing's sarcoma is an aggressive small round blue cell tumor typically arising in bone or soft tissues of children and young adults. Primary involvement of the prostate is exceptionally rare, with only a handful of cases reported. The unusual site and nonspecific clinical presentation often delay diagnosis. We report the case of a 35-year-old male patient who initially presented with progressive lower back pain of two months' duration, without neurological deficits. The pain was accompanied by urinary hesitancy and abdominal discomfort. Imaging revealed a markedly enlarged prostate (13.2 × 11.1 × 18.1 cm) with heterogeneous enhancement, cystic degeneration, and compression of adjacent pelvic structures. PET-CT demonstrated intense fluorodeoxyglucose (FDG) uptake in the prostate and distant metastases involving the lungs and liver. Histopathology of a core biopsy showed sheets of small round blue cells with hyperchromatic nuclei and scant cytoplasm, along with rosette formation. Immunohistochemistry (IHC) was positive for CD99, FLI-1, and NKX2.2, with a high Ki-67 proliferative index (80%). Fluorescence in situ hybridization (FISH) confirmed an EWSR1 gene rearrangement, establishing the diagnosis of Ewing's sarcoma of the prostate. The patient was started on multimodality VAC-IE (vincristine, doxorubicin, and cyclophosphamide alternating with ifosfamide and etoposide) chemotherapy. Given the presence of systemic metastases at diagnosis, the prognosis remains guarded, but early initiation of therapy was pursued to achieve disease control. This case underscores the diagnostic challenge of Ewing's sarcoma in an unusual site such as the prostate, particularly when presenting with back pain rather than urological complaints. Persistent or unexplained back pain in young adults should prompt consideration of rare malignancies. Comprehensive imaging, histopathology, IHC, and molecular analysis remain indispensable for diagnosis. Early recognition and a multidisciplinary treatment approach are essential to improving outcomes in this aggressive disease.