Secondary osteosarcoma following radiotherapy presenting with clival metastasis and abducens palsy: a case report

Radiation-induced secondary osteosarcoma is an uncommon but highly aggressive malignancy and represents a serious long-term complication of radiotherapy. The latency period is often several years, and the tumors are usually refractory to conventional chemotherapy, leading to poor outcomes. Clival metastasis from osteosarcoma is exceptionally rare, and to our knowledge, it has not previously been reported in radiation-induced cases. We report a 55-year-old Turkish male who had undergone surgery and adjuvant long-course chemoradiotherapy for rectal adenocarcinoma ten years earlier. He presented with progressive left hip pain, and imaging showed a destructive pelvic mass in the left iliac bone, while biopsy confirmed secondary osteosarcoma. He received three cycles of neoadjuvant cisplatin and doxorubicin (cisplatin 30 mg /m 2 days 1–3 and doxorubicin 25 mg/m 2 , days 1–3), but the disease progressed with new bone lesions, and therefore he underwent left hemipelvectomy. However, further progression occurred with vertebral, lung, lymph node, and peritoneal metastases. During follow-up, he developed diplopia due to right abducens nerve palsy, and cranial MRI revealed contrast-enhancing metastases in the clivus and occipital condyles. Consequently, he received palliative radiotherapy (8 Gy, single fraction) to the skull base, which led to partial improvement of diplopia and cranial nerve palsy. This case underscores the aggressive clinical course and unusual metastatic spread of radiation-induced osteosarcoma, with the clivus representing an extremely rare site of involvement. Timely recognition and local treatment of skull base metastasis can provide symptomatic relief and may prevent life-threatening complications. To the best of our knowledge, this is the first reported case of clival metastasis arising from a radiation-induced osteosarcoma.