Giant cell tumor (GCT) of bone is a benign but locally aggressive tumor that usually involves the epiphysis of long bones.¹Rarely, these tumors metastasize to the lung, and these metastases generally have the same benign histological appearance as the primary tumor. Multicentric giant cell tumor (M-GCT) is rarer. We herein report a case of M-GCT involving the left distal radius, with retroperitoneal metastasis, and subsequent lesions in the left proximal and distal femur. The patient and family members were informed that data concerning the case would be submitted for publication, and they consented.

In 2001, a 37-year-old male presented to doctors in Guangzhou (China) having experienced 1 month of left distal forearm pain and limited range of motion of the wrist. The pain worsened at night and was not relieved by non-steroidal anti-inflammatory medication. A radiograph showed a lytic lesion involving the epiphysis and metaphysis of the left distal radius. A biopsy was performed and a GCT was diagnosed. Curettage and cementation was performed. The diagnosis after surgery was a benign GCT (Figure 1A).

In 2005, the patient presented to our clinic with a painful enlarging mass on the distal part of his left forearm. Radiographs and computed tomography (CT) scanning showed a lytic lesion around the cement. Emission computed tomography (ECT) showed no other lesion except the one present in the left distal radius. A biopsy was performed and thediagnosis was the recurrence of benign GCT (Figure 1B–1E). The patient underwent a wide local excision of the tumor, and received an autologous fibular transfer with plate fixation. The histological findings were consistent with a benign GCT, consisting of mononuclear cells and multinucleated giant cells. Atypical mitoses or cytological atypia were not present. The findings for microbiological examination were also negative.

　　InNovember,, 2010, the patient presented to the hospital with an abdominal mass on his right side. CT scanning of the abdomen showed a 15 cm×12 cm×10 cm soft, smooth mass in the retroperitoneal region that was in close proximity to the kidney (Figure 1F). Serum calcium, phosphate, and alkaline phosphatase levels were normal. The retroperitoneal mass was completely removed. The histopathological finding was a GCT with strong aggressiveness and invasion of the right kidney cortex (Figure 1G). A CT scan showed no metastasis to the lungs. No adjuvant treatment was given. An immunohistochemical analysis was performed to rule out mesothelioma. The results of the analysis showed that the tumor was CD68 (+), vimentin (+), Ki67 <5%, EMA (-), calretinin (-), MC (-), CK5/6 (-), P53 (-), P63 (-), S-100 (-), TTF-1 (-), CD34 (-), CEA (-). This indicated that the tumor was a histiocytoma and not a retroperitoneal mesothelioma.