Giant Cell Tumor of Bone after Denosumab Chemotherapy Mimics Osteosarcoma

Purpose: Giant cell tumor (GCT) is a common neoplastic pathology of predominantly long bones, usually seen in young adults. Abundant literature is available regarding imaging and histopathologic characteristics of this tumor. However, to the best of our knowledge, very limited literature is available (none in radiology) on imaging and histopathology findings of GCT of bone after denosumab chemotherapy that can present a diagnostic challenge histopathologically as well as on imaging. This study describes the radiography and histopathology findings of GCT following denosumab chemotherapy in five patients. It also points out a few differentiating radiographic features with other malignant osteoid-producing lesions like osteosarcoma.

Methods and Materials: This was a nonstatistical retrospective observational study, performed in Deenanath Mangeshkar Hospital, a tertiary care center in India. Five patients with histopathologically proven GCT from 2013 to 2018 were studied who underwent three cycles of subcutaneous denosumab chemotherapy in our hospital. Both pre- and postchemotherapy radiographs were obtained in our department. All of them underwent surgery. Histopathologic correlation of the findings was subsequently performed on the resected specimens. All clinical, imaging, and histopathologic records were retrieved from the Picture Archiving and Communication System.

Results: Among these five patients, four were male and one was female, ranging in age from 16 to 35 years (mean age: 24.2 years). Two patients in the initial radiographic evaluation had GCT (proven on subsequent biopsy) of the proximal humerus, one of the distal tibia, one of the olecranon, and one of the lower femur. All patients presented for follow-up after completion of three cycles of denosumab chemotherapy with complaints of relative hardening of swelling. Follow-up radiographs revealed extensive peripheral and central sclerosis (new bone formation) within the previous lytic lesions without periosteal reaction or cortical destruction or a soft tissue component. Histopathologic evaluation of resected specimens revealed extensive mature bony matrix formation.

Conclusion: Extensive sclerosis is a side effect of denosumab chemotherapy that can mimic osteoid-producing lesions like osteosarcoma on imaging and histopathology if previous clinical or drug history is not available. Knowledge about the imaging features of GCT after denosumab chemotherapy is essential to avoid confusion.