Telomerase Activity in Giant Cell Tumors of Bone

H3F3 mutation status of giant cell tumors of the bone, chondroblastomas and their mimics: a combined high resolution melting and pyrosequencing approach

Behjati et al recently described recurrent mutations of H3F3 genes in giant cell tumors of the bone and chondroblastomas. Both these entities belong to the spectrum of giant cell-rich bone lesions, often presenting a diagnostic challenge for the pathologist. Our aim was to investigate the value of searching for H3F3 mutations in the diagnosis of giant cell tumors of the bone and giant cell-rich chondroblastomas. Two hundred eighty-one bone lesion samples, including 170 giant cell tumors of the bone, 26 chondroblastomas and 85 other giant cell-rich and/or epiphyseal tumors, were analyzed. Mutation status was determined using first high resolution melting screening and then mutation profiling pyrosequencing. Mutational status was compared with clinical data and, for giant cell tumors of the bone, with p63 immunostaining status. As histone methylation changes have been reported in association with H3F3 mutations, the methylation status of lysine 37 was investigated. H3F3A and H3F3B were found in 85% of giant cell tumors of the bone and 88% of chondroblastomas. In addition to the major G35W mutation, we found two rare H3F3A mutations: one G35R and one G35V. Among the other tumors studied, we only found H3F3A gene mutations in two cases of 'dedifferentiated chondrosarcoma mimicking giant cell tumor of the bone'. A H3F3B mutation was also observed in one case of dedifferentiated chondroblastoma. P63 expression in giant cell tumors of the bone seems to be associated with H3F3 gene mutations (P=0.004). H3F3 mutations did not correlate with clinical data, outcome or methylation changes in Lysin 37. In conclusion, H3F3 mutations are sensitive and specific markers of giant cell tumors of the bone and chondroblastomas. High resolution melting and pyrosequencing procedures are high-performance tools in this context. Determination of H3F3 mutation will allow reclassification of some entities belonging to the spectrum of giant cell-rich lesions.

Clival giant cell tumor - A rare case report and review of literature with respect to current line of management

Giant-cell tumor (GCT) involving the skull base is rare. Sphenoid bone is the most commonly involved bone followed by petrous temporal bone. Histopathology and radiological features of these lesions are similar to GCT involving bone elsewhere. Unlike other sites, skull base is not an ideal site for the radical surgery. Hence adjuvant treatment has pivotal role. Radiation therapy with intensity-modulated radiation therapy, stereotactic radiosurgery or chemotherapy with adriamycin are promising as described in some case reports. Bisphosphonates showed good control in local recurrence. In vitro studies with Zolendronate loaded bone cement and phase 2 trials of Denosumab showed hopeful results, may be useful in future.

Giant cell tumor of bone

EDUCATIONAL OBJECTIVES As a result of reading this article, physicians should be able to: 1. Identify at-risk populations for giant cell tumor of bone. 2. Recognize the biology that drives giant cell tumor of bone. 3. Describe modern surgical and adjuvant techniques to effectively treat giant cell tumor of bone. 4. Recognize the complications associated with radiation therapy, poor resection, and adjuvant treatments. Giant cell tumor of bone (GCT) is a benign, locally aggressive bone tumor. Giant cell tumor of bone primarily affects the young adult patient population. The natural history of GCT is progressive bone destruction leading to joint deformity and disability. Surgery is the primary mode of treatment, but GCT has a tendency to recur locally despite a range of adjuvant surgical options. Pulmonary metastasis has been described. However, systemic spread of GCT rarely becomes progressive, leading to death. This review presents the clinicopathologic features of GCT and a historical perspective that highlights the current rationale and controversies regarding the treatment of GCT.

Non-telomeric activities of telomerase

Recent results suggest that telomerase is involved in many more cellular processes than merely telomere elongation. These include telomere-independent anti-apoptotic, cytoprotective and pro-proliferative effects of telomerase or protection of mitochondrial DNA against oxidative stress. Telomerase also participates in DNA repair and its essential subunits, hTR and hTERT, are able to modulate independently the cell's response to DNA damage. Recent high throughput analyses of gene expression showed that hTERT expression modulates expression of about 300 genes, including genes involved in the regulation of cell cycle progression, proliferation and differentiation. Besides the well-known telomerase catalytic activity of RNA-dependent DNA polymerase, its RNA-dependent RNA polymerase activity was recently described in association with the RNA subunit of mitochondrial RNA processing endoribonuclease, thus suggesting involvement of telomerase in RNA interference processes. These recent discoveries open novel possibilities and entirely unexpected research perspectives, branching off from the mainstream telomere and telomerase research.

Cytogenetic analysis of 101 giant cell tumors of bone: nonrandom patterns of telomeric associations and other structural aberrations

Giant cell tumor of bone (GCTB) is a benign but locally aggressive tumor with metastatic potential. We performed cytogenetic analysis on 101 GCTB from 92 patients. Karyotypes were obtained from 95 tumors, 47 of which had clonal aberrations. The majority of the cytogenetically abnormal GCTB had multiple, up to 28 per tumor, clones. Clonal telomeric associations (tas) and other structural and numerical changes were found in about 70, 60, and 30%, respectively, of clonally abnormal tumors. Forty-seven aberrations were recurrent, of which 35 are novel. The vast majority of the recurrent aberrations were tas, confirming the important role of telomeric fusions in the development of GCTB. The frequency of tas in GCTB cultures increased with passaging, suggesting a selective advantage of tas-positive cells in vitro. The termini most frequently involved in tas were 22p, 13p, 15p, 21p, 14p, 19q, 1q, 12p, 11p, and 20q. The frequency of tas (irrespective of their clonality) was significantly higher in tumors carrying clonal changes, indicating that tas are precursors of other types of aberrations. In line with this assumption, the chromosomes preferentially involved in tas in a given tumor were also the ones most often affected by other rearrangements. We did not find the previously reported amplicon in 20q11.1, assessed by fluorescence in situ hybridization in 10 tumors. Nor did we find any association between cytogenetic features and adverse clinical outcome. Thus, local recurrences probably depend more on the adequacy of surgical treatment than on the intrinsic biology of the tumors.

Telomere-maintenance mechanisms in soft-tissue malignant fibrous histiocytomas

BACKGROUND

Sarcomas are distinct from carcinomas in that a substantial portion of them use the alternative lengthening of telomeres (ALT) mechanism to maintain their telomeres. The present study clarifies the prevalence of the ALT mechanism and examines the prognostic importance of telomere factors in soft-tissue malignant fibrous histiocytomas.

METHODS

We investigated a series of forty-three soft-tissue malignant fibrous histiocytoma samples from forty-three patients with regard to telomere length, telomerase activity, and human telomerase reverse transcriptase (hTERT) mRNA expression. Tumor samples were obtained from surgical specimens and were stored at -80 degrees C until use. Univariate analysis of the tumor samples from patients for whom data were available on age, sex, histological grade, tumor size, surgical margin, recurrence, and telomere factors was performed with use of the log-rank test. Multivariate analysis with only significant variables was then performed.

RESULTS

Telomerase activity was detectable in 79.1% of the tumor samples, hTERT expression was demonstrated in 90.7% of the tumor samples, and evidence of engagement of the ALT mechanism of telomere length maintenance was observed in 32.6% of the tumor samples. Among the variables tested, ALT-positive status emerged as the only independent prognostic factor for death of the patient (hazard ratio, 0.275; 95% confidence interval, 0.104 to 0.724; p=0.0089). There were no significant differences in survival rates between patients with ALT-positive, telomerase-positive tumors and those with ALT-positive, telomerase-negative tumors (p=0.301) or between patients with ALT-positive tumors that showed above-average telomerase activity and those with ALT-positive tumors that showed below-average telomerase activity (p=0.900). Therefore, telomerase activity does not affect the prognosis in patients with ALT-positive malignant fibrous histiocytoma. High telomerase expression is associated with a poor prognosis in patients with ALT-negative malignant fibrous histiocytoma (p=0.0027).

CONCLUSIONS

More detailed analysis will be needed to identify the most valuable prognostic factor in patients with malignant fibrous histiocytoma, and a more thorough understanding of telomere biology may give an indication of telomere-targeting therapy in the future.

Distribution and prognostic significance of human telomerase reverse transcriptase (hTERT) expression in giant-cell tumor of bone

Giant-cell tumor of bone is considered a benign, locally aggressive and rarely metastasizing neoplasm of bone. Specific microscopic or radiographic findings that reliably predict behavior have remained elusive. However, recent evidence suggests that activity of the telomerase enzyme complex correlates with recurrence in giant-cell tumor, although the subset of cells with telomerase activity in these heterogeneous tumors has not been defined. In the present study, we investigated whether immunostaining for human telomerase reverse transcriptase, a component of the telomerase complex, correlates with outcome in giant-cell tumor and the distribution of telomerase reverse transcriptase staining in these tumors. We analyzed 58 cases of giant-cell tumor for the presence and pattern of telomerase reverse transcriptase immunostaining, presence of soft tissue involvement and the type of initial surgery, and correlated these findings with recurrence-free survival and metastasis-free survival. Specific staining with telomerase reverse transcriptase was present in 20 out of 58 tumors (35%) in the nuclei of mononuclear cells and, occasionally, osteoclast-like giant cells. Furthermore, positive telomerase reverse transcriptase immunohistochemistry correlated with recurrence-free survival (P=0.02), whereas the presence of soft tissue extension (P=0.3) and the type of initial surgery (P=0.2) did not. Only soft-tissue extension significantly correlated with metastasis-free survival (P=0.003). Therefore, telomerase reverse transcriptase expression may predict recurrence in giant-cell tumor insofar as positive immunostaining correlates with shorter recurrence-free survival and may be a useful prognostic marker to stratify patients to more aggressive treatment protocols.