Multicentric metachronous giant cell tumor of the femur: a rare case report and review of the literature.

Background: Giant cell tumor of bone (GCTB) is a benign but locally aggressive osteolytic neoplasm that most commonly presents as a solitary lesion in long bones. Multicentric GCTB is rare, comprising fewer than 1% of all cases, and metachronous involvement of two distinct regions within the same bone is exceptionally uncommon. Case presentation: We report the case of a 22-year-old man who initially presented with a 2-year history of right knee pain. Radiologic and histopathologic evaluation confirmed a Campanacci grade III GCTB of the distal femur, which was treated with intralesional curettage, polymethylmethacrylate augmentation, and adjuvant radiotherapy. Seven months later, he developed new-onset right hip pain. Imaging revealed a separate osteolytic lesion of the proximal femur. Histopathology confirmed a second GCTB lesion, establishing the diagnosis of multicentric metachronous disease. Clinical discussion: The development of a second histologically confirmed GCTB within the same femur shortly after treatment of the primary lesion represents a rare diagnostic and therapeutic challenge. Distinguishing metachronous multicentric disease from intramedullary skip lesions and metastatic or metabolic bone disease is critical, as management and prognosis differ substantially. The recommended treatment for GCTB is curettage, but this may not be possible when the lesion is located in the proximal femur. Conclusion: This case highlights an exceptionally rare presentation of a metachronous, multicentric GCTB occurring in different regions of the same long bone. Vigilant long-term radiologic surveillance is essential.