Sclerosing epitheloid fibrosarcoma (SEF) is an extremely rare soft tissue sarcoma arising from connective tissue cells of mesenchymal origin. SEF mostly occurs in extraosseous sites in the soft tissue; however two cases of primary localization in the bone have been described. Despite benign cytological features the clinical course is complicated by a high local recurrence rate and late metastases. SEF represents a clinically challenging entity especially because no standardized treatment regimens are available.

We report a 16-year old female patient who showed persistent load-dependent pain focused on the right proximal tibia. Radiological evaluation revealed an osteolytic lesion and the diagnosis of a benign bone cyst was consented. The tumor was surgically removed. Only after recurrence of the tumor and repeated histopathological analysis diagnosis of SEF could be established.

Because of the bone localization of the tumor the patient underwent standardized neoadjuvant chemotherapy analogous to the European-American EURAMOS-1 protocol for the treatment of osteosarcoma followed by tumor resection and endoprothesis. Histopathological analysis of the resected tumor showed > 90% vital tumor cells suggesting no response to the neoadjuvant chemotherapy. Therefore, therapy was reassigned to the CWS protocol of the German Society for Pediatric Oncology and Hematology (GPOH) for treatment of soft tissue sarcoma. To date, the patient is alive and no metastases of the primary tumor can be detected.

SEF represents a taunting clinical entity due to deceptive histopathological features and rare occurrence. Localization in the bone represents an additional challenge with regards to the therapeutical approach. Standardized treatment regimens are currently not available for SEF. This case report, to our knowledge, is the first outlining a therapeutic approach in detail. Our data suggest that SEF may be resistant to a chemotherapy regimen containing Cisplatin, Doxorubicin and Metho-trexate despite close association to the bone, possibly indicative of the soft tissue histogenesis of this tumor. The response to the soft tissue sarcoma targeting CWS chemotherapy remains to be determined.