Osteoblastoma: A Case Series

Background: Osteoblastoma (OB) is a rare tumor constituting only 1% of all primary bone tumors. It typically occurs in males, in the second decade of life, and primarily affects the vertebral column and long bones. While it is generally considered benign due to its slow-growing nature and inability to metastasize, OB can occasionally exhibit aggressive features of growth, causing significant bone destruction, infiltration of the soft tissues, and epidural extension. The current treatment of choice is complete surgical resection, reserving radiotherapy, and chemotherapy for aggressive or surgically unresectable tumors. Next-generation sequencing (NGS) is not included in the typical evaluation and may offer novel insight into genetic alterations associated with OB. Case Information: With the description of these three cases, we aim to highlight the extraordinarily diverse ways that OB can present and behave, from a highly aggressive course in the cervical spine that progressed even after 4 surgeries to a dormant disease affecting the clavicle, requiring only local curettage for diagnosis and no further treatment. Additionally, we present genetic information acquired by NGS testing, not conventionally part of the work-up for OB. This case series examined NGS results, surgical margin outcomes, treatment modalities, imaging, and relevant scientific literature for each case, as well as pertinent information from each patient’s medical history. Of the three cases we reviewed, all were female, ages 8, 9 and 11. Tumor locations varied, affecting the thoracic vertebrae T8-9, cervical vertebra C7, and clavicle. The disease courses of these patients ranged from inoperable spinal tumor necessitating radiotherapy to residual disease after 4 vertebrectomy surgeries to dormant disease of the clavicle with resolution after curettage. Furthermore, the differential diagnoses considered among these cases consisted of primary aneurysmal bone cyst, chondroblastoma, osteosarcoma, Ewing sarcoma, lymphoma, rhabdomyosarcoma, giant cell tumor, and chronic recurrent multifocal osteomyelitis, demonstrating the potential difficulty in diagnosing OB. NGS testing was performed on tumor samples of 2 out of 3 of the patients and revealed a WWTR1-FOSB translocation and a germline ATM mutation. The two patients with vertebral involvement experienced progressive disease within 7 months postoperatively and the remaining patient presented with normally maturing bone 3 months postoperatively. Conclusions: This case series emphasizes the capability of OB to present and progress in incredibly diverse ways. Moreover, there is currently a lack of knowledge regarding the genetic drivers of this disease process and we believe that NGS testing may assist in furthering the genetic characterization of this tumor.