Malignant transformation of metastatic giant cell tumor of bone in a patient undergoing denosumab treatment: A case report

Malignant Giant Cell Tumor of Bone: A Clinicopathologic Series of 28 Cases Highlighting Genetic Differences Compared With Conventional, Atypical, and Metastasizing Conventional Tumors

Giant cell tumors of bone are locally aggressive, frequently harbor H3F3A p.G34W mutations, and rarely undergo malignant transformation. The pathogenesis of malignant transformation remains incompletely characterized. Herein, we present 28 malignant giant cell tumors of bone from 14 males and 14 females, aged 16 to 65 (median 39) years. Primary sites included long bones (n=20), pelvis (n=3), vertebrae (n=2), and rarely rib, phalanx, and cuneiform (n=1 each). Sixteen (62%) of 26 tumors with available history represented malignant transformation or recurrence of conventional giant cell tumors of bone, at intervals of 1.3 to 35 (median 7.3) years before malignant transformation. Eight of 15 patients with available treatment history received denosumab before a diagnosis of malignancy. Ten (38%) of 26 tumors with available history likely arose de novo, including 7 with conventional areas and 3 H3F3A -mutant sarcomas lacking conventional giant cell tumor of bone. Of 28 malignant giant cell tumors of bone, 18 (64%) and 10 (36%) harbored osteoblastic and chondroblastic elements, respectively. Among 23 tumors with available genetic testing or surrogate immunohistochemistry, 17 (74%) were p.G34W-mutant, whereas other tumors carried H3F3A p.G34L (n=2), p.G34V (n=2), and p.G34R (n=1) alterations; 1 tumor harbored H3F3B p.K116E and p.R117S in cis. Seven (70%) of 10 malignant giant cell tumors of bone showed complex copy number alterations by single nucleotide polymorphism (SNP) array, DNA next-generation sequencing (NGS), and/or karyotype analysis. In contrast, complex chromosomal alterations were lacking in 32 conventional giant cell tumors of bone tested (24 by karyotype, 7 by SNP array, 1 by DNA NGS), 3 atypical giant cell tumors of bone with isolated marked nuclear atypia (2 by karyotype, 1 by SNP array) and 3 metastasizing conventional giant cell tumors of bone (2 by DNA NGS, 1 by karyotype). Clinical follow-up was available for 20 patients (71%), and one additional patient had metastases at presentation. Overall, 14 of 21 patients (67%) developed metastases, and 10 of 20 patients with follow-up (50%) died of disease at 2 months to 9.6 years (median 7 mo). Most patients were treated with chemotherapy; 1 patient (PD-L1 TPS >95%) was treated with pembrolizumab, with complete clinical response of metastatic disease at 2.5 years. In conclusion, malignant giant cell tumors of bone typically arise from long bones, harbor osteosarcomatous and/or chondrosarcomatous differentiation, and show significant risk for distant metastasis and demise. Our data suggest that copy number analysis may be useful in distinguishing malignant giant cell tumors of bone from their conventional, atypical, and metastasizing conventional counterparts.

Recurrent benign fibrous histiocytoma of the bone benefits from denosumab followed by malignant transformation: a case report

Benign fibrous histiocytoma of the bone (BFHB) is a rare mesenchymal tumor, representing less than 1% of all benign bone tumors. This controversial entity is characterized by a mixture of fibroblasts arranged in a storiform pattern, varying amounts of osteoclast-type giant cells and foamy macrophages. Curettage or simple resection is usually curative. However, it was reported that up to 11% of the patients suffer from relapse. Here, we report a case of malignant transformation of BFHB after long-lasting disease stabilization under denosumab therapy.

Clinicopathological and histological analysis of secondary malignant giant cell tumors of bone without radiotherapy

Giant cell tumor of bone (GCTB) is an intermediate bone tumor that rarely undergoes malignant transformation. Secondary malignant GCTB (SMGCTB) is defined as a lesion in which high-grade sarcoma occurs at the site of previously treated GCTB. The present study retrospectively reviewed the medical records of patients with GCTB treated at Okayama University Hospital between April 1986 and April 2020. The clinicopathological and histological features of patients with SMGCTB without prior radiotherapy were investigated. A total of three patients (4%) with SMGCTB were detected, and the tumor sites were the distal ulna, distal femur and sacrum. Two of the patients had been treated with curettage and bone graft, and one had been treated with denosumab. In all cases, the lesions were made up of two components, the conventional GCTB component and the malignant component. The Ki67 labeling index was higher in the malignant components of SMGCTB and metastatic lesions compared with that in primary and recurrent conventional GCTB, or the conventional GCTB component of SMGCTB. Moreover, p53 expression was higher in these same components in patients who underwent curettage and bone grafting; however, there was no difference in the patient that received denosumab treatment. In this patient, clinical cancer genomic profiling revealed loss of CDKN2A, CDKN2B and MTAP expression. All three patients developed distant metastasis. The patients with SMGCTB in the ulna and femur died 13 and 54 months after detection of malignant transformation, respectively. The patient with SMGCTB in the sacrum received carbon-ion radiotherapy to the sacrum and pazopanib; the treatment was effective and the patient was alive at the last follow-up 3 years later. In conclusion, p53 may be associated with malignant transformation in GCTB. Future studies should investigate the association of between denosumab treatment and malignant transformation, as well as molecular targeted therapy to improve the clinical outcomes of SMGCTB.