Osteoblastoma-like osteosarcoma: High-grade or low-grade osteosarcoma?

AIMS: Osteoblastoma-like osteosarcoma is a rare variant of osteosarcoma (1% of all osteosarcomas), histologically similar to osteoblastoma. In the current WHO classification osteoblastoma-like osteosarcoma is classified within the group of conventional (high-grade) osteosarcomas. However, several published cases have been actually regarded as low-grade malignant tumors. Since strict morphologic criteria to distinguish between low-grade and high-grade lesions are not available we reviewed our series of osteoblastoma-like osteosarcomas in the attempt to identify clinical and morphologic features predictive of aggressiveness.

METHODS AND RESULTS: We retrieved 15 cases of osteoblastoma-like osteosarcoma from the files of the Istituto Ortopedico Rizzoli. Patients received various treatments. Five patients developed metastasis, and 5 patients developed local recurrences (all after incomplete surgery). Eleven patients were alive without disease, while 4 patients died of their disease. Statistical analysis revealed a statistically significant (p = 0.048) lower disease-free survival in patients with areas of conventional (high-grade) osteosarcoma.

CONCLUSIONS: With the important limitation of small cohort of patients, the presence of areas of conventional (high-grade) osteosarcoma is the only parameter to predict the aggressiveness of osteoblastoma-like osteosarcoma. This article is protected by copyright. All rights reserved.