Primary desmoplastic small round cell tumor of the femur.

Desmoplastic small round cell tumor (DSRCT) is a rare malignant neoplasm typically involving the abdominal cavity of a young male. Extra-abdominal occurrence of this tumor is very rare. We report a 10-year-old girl with primary DSRCT arising within the left femur. The patient presented with knee pain, and radiological findings were strongly suggestive of osteogenic sarcoma. In addition to the typical microscopic appearance and immunophenotype, RT-PCR demonstrated the chimeric transcript of EWS-WT1, which is diagnostic of DSRCT. Pulmonary metastases were present at initial staging studies, but no abdominal or pelvic lesion was present. Despite chemotherapy and complete tumor excision, the patient developed progressive lung and bone metastases and died 3 years after initial presentation. This is the second reported case of primary DSRCT of bone with genetic confirmation.