Primary Bone Sclerosing Epithelioid Fibrosarcoma: A Case Report and Literature Review.

Sclerosing epithelioid fibrosarcoma (SEF) is an extremely rare soft tissue sarcoma. Primary involvement of the bone, particularly the spine, is exceptional, with only isolated cases described. We report a very rare case of primary spinal SEF occurring in a 30-year-old male who presented with chronic back pain. MRI revealed a mass involving the thoracic vertebrae. CT-guided biopsy showed a densely sclerotic stroma containing atypical spindle-to-epithelioid cells arranged in cords and nests. Immunohistochemistry demonstrated strong positivity for mucin-4 (MUC4) and epithelial membrane antigen, with negative staining for S100, desmin, and CK AE1/AE3, confirming the diagnosis of SEF. Surgical excision and spinal fixation were initially planned; however, the patient relocated abroad before surgery and instead received high-dose proton-beam radiotherapy alone. He remains under follow-up in 2024 without surgical intervention. This case emphasizes the significance of including primary bone SEF in the differential diagnosis of thoracic spinal masses, particularly in individuals experiencing chronic back pain. Timely identification and precise diagnosis with specific immunohistochemistry are crucial in guiding an appropriate treatment strategy. Our analysis of 38 cases, including our case, showed a male predominance, spinal involvement, and a high MUC4 positivity rate, reinforcing its role as a key diagnostic marker.