Dedifferentiated soft tissue leiomyosarcoma with heterologous osteosarcoma component: case report and review of the literature.

Background: Soft tissue dedifferentiated leiomyosarcoma with heterologous osteosarcomatous component is an extremely rare entity described in only few cases in the literature.

Case presentation: We report the case of a 65-year-old male patient who, after initial inadequate surgery of a tumor of the left forearm, developed local recurrence that was treated with neoadjuvant chemotherapy, surgery and postoperative radiation therapy. Histologically the tumor showed an abrupt separation of two different patterns. One component consisted of interlacing fascicles of spindle cells with cigar-shaped nuclei strongly positive for smooth muscle actin, desmin and H-caldesmon. The other component consisted of a high-grade pleomorphic sarcoma with osteoid and chondroid matrix production, which positive for SATB2. Thus, a final diagnosis of dedifferentiated leiomyosarcoma was rendered. Fifteen months after treatment, the patient presented further local and distant relapse with pulmonary metastases and died 23 months after the first presentation.

Discussion and conclusions: Dedifferentiated leiomyosarcoma is a highly malignant neoplasm with a poor outcome. Extensive sampling of soft tissue leiomyosarcomas is recommended to detect possible dedifferentiated areas as they represent a crucial prognostic parameter.