Heavily ossified renal mass as the initial presentation of primary renal osteosarcoma: a case report

Primary renal osteosarcoma (PRO) is a rare extraskeletal malignancy, accounting for less than 1% of soft-tissue sarcomas and fewer than 50 reported cases to date. We present the case of a 47-year-old male who presented with six months of progressive right flank pain and an abdominal lump. Initial imaging with plain radiography and contrast-enhanced computed tomography urography revealed a large, heterogeneously enhancing right renal mass characterised by extensive, confluent, dense intratumoral calcifications with a bone-like appearance, mediastinal displacement of adjacent viscera, calcified retroperitoneal lymph nodes, and peritoneal deposits suggestive of metastatic disease. The radiologic differential diagnosis included renal cell carcinoma with dystrophic calcification, calcified renal tuberculosis, and stone disease. Diagnostic laparoscopy with biopsy revealed pleomorphic spindle-to-epithelioid cells in disorganised sheets with characteristic lace-like eosinophilic osteoid. Immunohistochemical analysis confirmed the diagnosis by demonstrating SATB2 positivity and negativity for MDM2, cytokeratin, PAX8, and CD34, with a high Ki-67 proliferation index, supporting a mesenchymal origin rather than sarcomatoid carcinoma. In view of peritoneal and lymph node involvement indicating metastatic disease, the patient was initiated on platinum-based combination chemotherapy with doxorubicin and cisplatin, completing three cycles with good tolerance. This case highlights the clinical, radiological, and pathological features essential for diagnosing PRO, a uniformly aggressive malignancy that typically presents at an advanced stage with poor prognosis. Definitive diagnosis requires comprehensive histopathological examination combined with targeted immunohistochemical panels to exclude alternative etiologies, including sarcomatoid renal cell carcinoma and renal tuberculosis. Multimodal management with radical surgical resection and platinum-based chemotherapy represents the current standard of care, though long-term outcomes remain limited.