Visualization of hidden soft-tissue recurrence of giant cell tumor of bone enabled by preoperative denosumab treatment: a case description.

An 18-year-old Japanese female presented to prior hospital with a 3-month history of pain in the right proximal lower leg and gradually progressive muscle weakness of the ankle dorsiflexion. A radiological examination suggested a bone tumor of the fibular head (Figure 1A,B), and the patient was then referred to our hospital. Magnetic resonance imaging (MRI) showed an expansile and osteolytic lesion in the proximal fibula with extraosseous extension (Figure 1C,D). After a needle biopsy, the lesion was diagnosed as a giant cell tumor of bone (GCTB), Campanacci grade III (1), and we performed a tumor resection. The intraoperat ive gross f indings revealed an extraosseous tumor involving the common peroneal nerve, and we dug out and preserved the nerve from the tumor (Figure 1E,F). The histopathological examination showed typical numerous osteoclast-like multinuclear giant cells and mononuclear neoplastic stromal cells (Figure 1G). Mononuclear neoplastic stromal cells showed immunopositivity for H3.3 G34W, characteristics of GCTB, but multinuclear giant cells were negative (Figure 1H). The patient was finally diagnosed as a GCTB. Although common peroneal nerve palsy temporarily occurred after the operation, it spontaneously recovered within approx. 6 months. Nineteen months after the surgery, plain radiographs of the right lower leg showed a tiny ossification in the soft tissue of the posterior to fibula stump (Figure 2A,B), MRI demonstrated a mass in the soft tissue anterior to the fibula stump (Figure 2C,D), and the lesions observed were considered a latent recurrence. Considering the intraoperative findings, we suspected that there was a possibility that spread recurrent tumors that were not visible to the naked eye were present around the preserved common peroneal nerve. Therefore, before the resection of the recurrent lesion, the patient underwent nine courses of preoperative denosumab treatment, injecting 120 mg of subcutaneous denosumab every four weeks with loading doses on days 8 and 15, for the purposes of visualizing the hidden recurrent tumors by mineralization and shrinking the recurrent tumor. Six months later, the recurrent lesion had shrunk in size and eggshell-like ossification appeared, and another ossification appeared in the surrounding soft tissue inferior to the fibula stump on plain radiographs (Figure 2E,F) and MRI (Figure 2G,H). We performed a marginal resection of Letter to the Editor