Can Osteoblastoma Evolve to Malignancy? A Challenge in the Decision-Making Process of a Benign Spine Tumor

Background: Osteoblastoma is a rare benign aggressive tumor, with one third occurring in the spine. Conversion of osteoblastoma to osteosarcoma is uncommon, and histologically proven conversion has been rarely reported. Case Description: Cases of 2 patients with rare occurrences of spinal osteoblastomas recurring and transforming into osteosarcomas are presented. Initial presentation, treatment, imaging, and histology findings are described. The outcomes of the patients following surgical intervention for histologically diagnosed osteoblastoma with subsequent transformation to osteosarcoma and relative management are described. A literature review of osteoblastoma converting to osteosarcoma also is provided. Conclusions: The rare occurrence of osteoblastoma converting to osteosarcoma imparts several lessons, including performing Enneking appropriate surgery for benign aggressive tumors (Enneking stage 3) and always performing a biopsy, particularly at the time of recurrence if imaging is not pathognomonic for a benign primary spine tumor.