Primary osteosarcoma of the kidney. Report of a case studied by immunohistochemistry, electron microscopy, and DNA flow cytometry.

A case of primary osteogenic sarcoma of the kidney is presented. The patient, a 75-year-old man, presented with flank pain, weight loss, and a lower lip lesion. Biopsy of the lip lesion showed metastatic sarcoma and nephrectomy revealed a primary osteogenic sarcoma. Ultrastructural and immunohistochemical studies confirmed the mesenchymal nature of the lesion and helped exclude sarcomatoid renal cell carcinoma from the differential diagnosis. Multiple samples of the primary tumor and metastatic deposits analyzed by DNA flow cytometry all showed a diploid DNA content. Clinically the tumor has pursued a slowly progressive course, with metastases.