Clinicopathological Features of a Series of 27 Cases of Post-Denosumab Treated Giant Cell Tumors of Bones: A Single Institutional Experience at a Tertiary Cancer Referral Centre, India.

Giant cell tumor of bone (GCTB) is mostly a benign tumor, but associated with recurrences and metastasis. Lately, denosumab is being utilized in the treatment of certain GCTBs. Twenty-seven tumors, analyzed in the present study, occurred in 16 males and 11 females (M: F = 1.45:1), in the age-range of 16 to 47 years (mean = 29.5, median = 29). Most tumors were identified in the tibia(6) and femur(6), followed by the humerus(3), radius(3), pelvis(3), fibula(3), sacrum(1), metacarpal(1) and metatarsal(1) bones. There were 18(66.6 %) primary and 9(33.3 %) recurrent tumors. Exact tumor size (19 cases) varied from 3.7 to 15 cm (mean = 7.8, median = 6.4). Eight of the 19 tumors (42.1 %) had size more than or equal to 8 cm. On histopathologic examination of post-denosumab treated specimens, more than half cases (15)(55.5 %) revealed complete absence of osteoclast-like giant cells (OCLGs) and 12 cases revealed residual OCLGCs. In addition, there was replacement by fibro-osseous tissue, including reactive woven bone or osteoid in most cases, followed by variable amount of spindle cells, hyalinisation, fibrosis and chronic inflammatory cells, including lymphocytes, macrophages and plasma cells. Post-treatment follow-up (25 cases, 92.5 %), over 7-27 months duration (median = 18), revealed 20 cases continuously disease-free. Five patients developed recurrences at 9, 12, 13, 14 and 18 months, respectively. Out of these, who underwent repeat surgical intervention, 4 patients are alive with no evidence of disease and a single patient, planned for a second surgery, is alive-with-disease. Denosumab was mostly offered to patients with large sized, borderline salvageable tumors, in order to decrease the morbidity of index surgical procedure, that led to disappearance of OCLGCs in most cases. Post-denosumab treated GCT cases appear as low grade osteosarcomas on histopathologic examination, but lack the clinical behaviour of an osteosarcoma, therefore may be considered as pseudo malignant bony lesions.