Abstract

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• Primary renal extra-osseous osteosarcoma is an exceedingly rare and deadly kidney neoplasm with only 27 reported cases to date. Extra-osseous osteosarcoma is a mesenchymal sarcoma that produces osteoid, but has no skeletal or periosteal involvement and most commonly arises in the lower extremities. Yet, it can arise in other locations such as the kidney. Extra-osseous osteosarcoma behaves as a separate entity from osseous osteosarcoma and should be treated as such. The treatment is surgical resection. Five year overall survival is 46% for local and 10% for metastatic disease. Additionally, 45%-50% of patients experience disease recurrence. We present a 77-year-old woman who underwent work up for recurrent gross hematuria and subsequently underwent radical nephroureterectomy for presumed upper tract urothelial cell carcinoma. However, pathologic analysis revealed a diagnosis of primary renal extra-osseous osteosarcoma. She is alive with no evidence of disease 30 months after surgery.