Primary fibroxanthosarcoma of the kidney presenting as fever of unknown origin.

Fibroxanthosarcoma is a tumor of soft tissues, mainly effecting the extremities, mediastinum and retroperitoneum. Primary fibroxanthosarcoma of the kidney is extremely rare and has been described in only 4 cases in the past. We present an additional patient, presenting with continuous spiking fever, with rapid deterioration of her condition due to widespread metastases and death within 4 months.