Histologically Confirmed Brain Metastasis Arising From Giant Cell Tumor of Bone: an Uncommon Entity and a Challenging Condition.

BACKGROUND Giant cell tumors of bone (GCTBs), while classified as indolent, are characterized by their locally aggressive nature and their ability to form metastases in rare cases, mainly in the lungs. To our knowledge, this case is the third reported case of GCTB central nervous system involvement in the literature. CASE REPORT We report the exceptional case of a 39-year-old patient with no significant medical history who presented with a GCTB of the left distal femur, treated with preoperative denosumab and surgical resection with massive prosthetic reconstruction. Fifteen months later, the onset of tremors and a partial seizure revealed a right parietal brain metastasis, histologically confirmed as a secondary site of GCTB. Management included surgical excision of the brain lesion, followed by close monitoring with brain MRI, without adjuvant radiotherapy. Before the present report, only 2 cases of GCTB metastasis involving the central nervous system have been reported, including an intramedullary thoracic lesion and bilateral parietal lesions. CONCLUSIONS This case is the third reported case of GCTB metastasis with central nervous system involvement, highlighting the importance of prolonged follow-up and an individualized multidisciplinary approach for these tumors, which usually metastasize to the lungs. Although these 3 case reports help to characterize this rare condition of secondary central nervous system involvement in GCTBs, they do not justify routine brain imaging or a set standard for follow-up strategies; instead, a multidisciplinary and individualized approach is recommended. The patient is currently in clinical and radiological remission.