Giant Cell Tumor With Atypical Imaging Implying Osteosarcoma

Giant cell tumor (GCT) of bone is benign and typically shows osteolytic changes on x-ray, whereas osteosarcoma is malignant and generally shows osteolytic and osteoblastic mixed images. We experienced a rare case of GCT with atypical radiological findings. The tumor found in the right knee of a 15-year-old girl comprised a wide range of osteoblastic and osteolytic lesion in medial femur. Technetium uptake, however, was detected only in osteoblastic part, and immunohistochemical staining of biopsy showed diffusely positive for antihistone G34W and almost negative for Ki-67. These results strongly suggest the tumor was GCT.