Delayed Metachronous Multicentric Giant Cell Tumor of Bone after a 16-Year Disease-Free Interval: A Case Report.

Introduction: Multicentric giant cell tumor (GCT) of bone is rare and usually occurs synchronously or within a few years of the primary lesion. Delayed metachronous presentation is exceedingly uncommon. Case Report: We present the case of a 48-year-old man with progressive left hip pain 16 years after wide resection and endoprosthetic reconstruction for GCT of the proximal right humerus. Imaging demonstrated well-defined lytic lesions involving the bilateral proximal femur, left iliac bones, with cortical breach in the periacetabular region and right iliac bone. Whole-body positron emission tomography computed tomography revealed no additional skeletal lesions or pulmonary metastases, and core needle biopsy confirmed GCT. Metabolic evaluation, including serum parathyroid hormone levels, was normal, excluding hyperparathyroidism-related brown tumors. Given the multicentric involvement of the bilateral pelvis and proximal femur, the anatomically complex periarticular location of the lesions, and the substantial morbidity associated with extensive surgical resection and reconstruction, a non-operative treatment strategy was considered more appropriate. The patient was therefore treated with six intravenous zoledronic acid infusions at monthly intervals. Conclusion: There is achieved complete pain relief, returned to unrestricted functional activity, and demonstrated radiological stabilization with progressive sclerosis and no disease progression at 4-year follow-up. This case highlights the unpredictable biological behavior of GCT, the possibility of very late metachronous multicentric disease, and the potential role of bisphosphonate monotherapy as a limb-preserving treatment option in carefully selected patients.