Giant cell tumor of ribs masking a huge soft tissue tumor: A potential diagnostic pitfall

Primary giant cell tumor originating in the rib is rare, resembling giant cell tumor in the epiphyseal region of long tubular bones morphologically and immunologically. However, this lesion poses a great challenge for diagnosis due to uncommon clinical and radiological presentation and histological heterogeneity. Here we report two cases of huge giant cell tumor of ribs presented as soft tissue mass. The first patient presented as a large expanding soft tissue mass in the right thoracic cavity attached to the 4th and 5th ribs with bone destruction. The second patient showed an ill-defined soft tissue mass in the left retroperitoneum. The maximum diameter of the lesions are greater than 15cm. Apart from the typical lesion with giant cell tumor evenly distributed among the mononuclear cells, there are secondary change including multiple hemorrhage cyst formation, irregular ossification and spindle cell proliferation, which mimics malignancies. H3.3 p.G34W immunohistochemistry and H3F3A mutation detected by Sanger sequencing supported the diagnosis of giant cell tumor. Our studies emphasized radiological and histological polymorphism and the diagnostic value H3F3A mutation, with a review of other published reports to assess radiological and pathological diagnosis and outcomes in case of misdiagnosis and overtreatment.