Leiomyosarcoma of the Bone: A Case Report on the Critical Role of Biomarkers in Differential Diagnosis.

Leiomyosarcoma of the bone (LMSB) is a rare type of sarcoma characterized by smooth muscle differentiation arising within the bone. We present the case of a 38-year-old female patient diagnosed with LMSB in the left distal femur. Histological examination revealed spindle-shaped and pleomorphic cells, with no evidence of cartilage or bone matrix formation. Immunohistochemical analysis demonstrated the tumor cell were positive for Smooth Muscle Actin, Desmin, and H-caldesmon. The integration of clinical presentation, imaging, morphological, and immunohistochemical findings confirmed the diagnosis of high-grade leiomyosarcoma of the bone. Postoperative pathological analysis further validated this diagnosis. One year after surgery, the patient remains stable, with no signs of recurrence or metastasis. Diagnosing leiomyosarcoma of the bone is particularly challenging due to the limitations of core needle biopsy samples. However, immunohistochemical evidence of smooth muscle differentiation plays a critical role in establishing the diagnosis.