Aggressive osteoblastoma with a secondary aneurysmal bone cyst treated with denosumab.

Osteoblastomas and aneurysmal bone cysts (ABC) are rare benign bone tumors that make up about 1%-2% of primary bone malignancies, typically occurring in young patients with a median age of 20 years, most commonly effecting the axial skeleton. ABCs may develop independently as primary lesions, or secondary to other bony lesions including osteoblastomas, chondroblastomas, and giant cell tumors. Treatment of unresectable or extensive osteoblastomas can be challenging. In 2013, the Food and Drug Administration (FDA) approved denosumab for the treatment of giant cell tumors of the bone due to its efficacy in these morbid bony lesions. Various case reports have shown that osteoblastomas can respond to denosumab. Furthermore, numerous ABC case reports have described the efficacy of denosumab in these situations. We herein describe a unique case of a young patient with an aggressive osteoblastoma and secondary ABCs who was successfully treated with denosumab.