Primary rhabdoid epithelioid sarcoma of the left thigh mimicking epithelioid rhabdomyosarcoma: A diagnostic pitfall

INTRODUCTION: Epithelioid sarcoma (ES) is a rare mesenchymal tumor, accounting for less than 1% of all adult soft-tissue sarcomas. The diagnosis of such malignancy is challenging. We reported a 31-year-old male diagnosed with rhabdoid ES that histologically mimicked epithelioid rhabdomyosarcoma in a 31-year-old male. CASE PRESENTATION: A 39-year-old male presented with pain in the left thigh. He had planned for open reduction internal fixation due to left femur fracture. During the surgery, the surgeon found abnormal appearance of the bone and the surrounding tissue. The histopathology examination showed spindle-to-polygonal epithelioid cells arranged in nodular pattern with necrotic areas. Immunohistochemistry examination revealed vimentin and CK positive expression, while myogenin was negative. Further immunostaining using CD34 and HMB45 were also negative. DISCUSSION: The diagnosis of ES based on only the clinical manifestation has proven to be difficult. Thus, the histopathology examination followed by immunohistochemistry is considered as the main modality for the diagnosis. Better understanding of clinical properties of ES will aid in deciding the best treatment for the patient.