Case report of a primary cystic sarcoma of the kidney, demonstrating fibrohistiocytic, osteoid, and cartilaginous components (malignant mesenchymoma).

The first case of a primary, cystic sarcoma of the kidney, containing fibrohistiocytic, osteoid, and cartilaginous elements (malignant mesenchymoma) is reported. The neoplasm occurred in a 29-year-old white woman, who had a right upper quadrant mass at least four years prior to presentation. Light and electron microscopy findings are presented. A 14-month follow-up revealed an extensive tumor recurrence in the right perirenal area with no apparent metastastic disease.