Osteosarcoma Arising from Iliac Bone Lesions of Hereditary Multiple Osteochondromas: A Case Report.

Introduction: Osteochondromas are benign tumors that arise primarily in the metaphyseal region of long bones. The malignant transformation rate is estimated to be less than 1% and 1-3% in solitary and multiple osteochondromas, respectively. Transformation to osteosarcoma is very rare. Little information is available on treatment or outcome. A rare case of osteosarcoma arising from hereditary multiple osteochondromas of the right iliac bone is reported. Case Presentation: A 66-year-old woman presented with recurrent right abdominal pain. Computed tomography (CT) showed a mass protruding into the pelvic cavity, 9 cm × 7 cm × 7 cm, with bone destruction and internal calcification in the right iliac bone. A CT-guided biopsy was performed, and the diagnosis was osteosarcoma. After one course of chemotherapy with doxorubicin and ifosfamide, extensive resection of the tumor was performed. The pathology showed proliferation of highly pleomorphic dysplastic cells with bone formation inside the tumor just below the osteochondroma tissue, which led to the diagnosis of osteosarcoma arising from the osteochondroma. Three years after surgery, there was no evidence of recurrence or metastasis, and the patient was able to walk unassisted. Conclusion: A case of osteosarcoma arising from an iliac lesion of hereditary multiple osteochondromas was described. Although no recurrence or metastasis has been observed 3 years after surgery, further follow-up is necessary due to the short time after surgery.