Giant Cell Tumor Developing in Paget's Disease of Bone: A Case Report with Review of Literature.

INTRODUCTION: Paget's disease of bone (PDB) is a disease of elderly characterized by disorganized bone remodeling. Development of secondary neoplasm in PDB is a known but rare phenomenon. Development of giant cell tumor in PDB (GCT-PDB) is extremely rare, and little is known about its etiopathogenesis and management. We present a case report of such a development with a review of the literature and the role of various new modalities of treatment available in the management of this rare condition.

CASE REPORT: A 40-year-old gentleman presented with back pain and on evaluation was diagnosed as a case of polyostotic PDB. He was treated with intravenous bisphosphonates, calcium, and vitamin D supplements. After an asymptomatic period of 3-year, he presented with a gluteal mass involving ilium and sacrum which was confirmed as GCT on biopsy. Serial angioembolization was attempted but mass progressed, so surgery performed with excision and curettage of the lesion. He presented with a local recurrence 2 years later with a large soft tissue component. He was started on denosumab, RANKL inhibitor, with the aim to downstage the lesion. The patient showed a good response after 6 doses with reduction in soft tissue mass followed by which he underwent surgery with partial T-1 internal hemipelvectomy and curettage of sacrum. Currently, the patient is asymptomatic at a follow-up of 15 months.

CONCLUSION: GCT-PDB is a rare phenomenon occurring mainly in polyostotic PDB and is associated with more severe manifestations of the disease. The management is challenging and requires multimodality management. Pharmacological agents include use of bisphosphonates and RANK ligand inhibitor - denosumab. Although surgery is the mainstay of treatment for GCT, other modalities of treatment such as RANK ligand inhibitors (denosumab), selective arterial embolization, or radiation therapy has to be used for inoperable cases or where surgery would be functionally too morbid, especially in cases of GCT-PDB where the disease affects more commonly the axial skeleton.