Successful Treatment with Denosumab of a Giant Cell Tumor of Bone in the Iliac Bone of an 84-Year-Old Man

We report a case of GCTB in an 84-year-old Japanese man who had a tumor in his left iliac bone and was treated safely with denosumab. The patient noticed a painful mass, with gradual enlargement, in his left low back next to the iliac region. Magnetic resonance imaging revealed that the tumor measured 94 × 66 × 90 mm and was located in the left iliac bone. Histologically, the tumor was composed of proliferative oval-shaped mononuclear cells, admixed with large number of osteoclast-like giant cells. Immunohistochemically, a strong positivity for histone 3.3 G34W mutant protein was observed in the nuclei of the mononuclear cells, confirming the diagnosis of GCTB. Because it was considered as unresectable tumor, the patient was treated with denosumab without any side effects