Genetic Alterations in Gliosarcoma and Giant Cell Glioblastoma

Understanding TERT Promoter Mutations: A Common Path to Immortality

Telomerase (TERT) activation is a fundamental step in tumorigenesis. By maintaining telomere length, telomerase relieves a main barrier on cellular lifespan, enabling limitless proliferation driven by oncogenes. The recently discovered, highly recurrent mutations in the promoter of TERT are found in over 50 cancer types, and are the most common mutation in many cancers. Transcriptional activation of TERT, via promoter mutation or other mechanisms, is the rate-limiting step in production of active telomerase. Although TERT is expressed in stem cells, it is naturally silenced upon differentiation. Thus, the presence of TERT promoter mutations may shed light on whether a particular tumor arose from a stem cell or more differentiated cell type. It is becoming clear that TERT mutations occur early during cellular transformation, and activate the TERT promoter by recruiting transcription factors that do not normally regulate TERT gene expression. This review highlights the fundamental and widespread role of TERT promoter mutations in tumorigenesis, including recent progress on their mechanism of transcriptional activation. These somatic promoter mutations, along with germline variation in the TERT locus also appear to have significant value as biomarkers of patient outcome. Understanding the precise molecular mechanism of TERT activation by promoter mutation and germline variation may inspire novel cancer cell-specific targeted therapies for a large number of cancer patients.

Radiotherapy plus concomitant temozolomide in primary gliosarcoma

Clinical guidelines for gliosarcoma (GSM) are poorly defined and GSM patients are usually treated in accordance with existing guidelines for glioblastoma (GBM), with maximal surgical resection followed by chemoradiation with temozolomide (TMZ). However, it is not clear yet if GSM patients profit from TMZ therapy and if O6-methylguanine-DNA-methyltransferase (MGMT) promoter methylation is crucial. We retrospectively evaluated 37 patients with histologically proven, primary GSM who had received radiation therapy since the temozolomide era (post-2005). Twenty-five patients (67.6 %) received combined chemoradiation with temozolomide, and 12 cases (32.4 %) received radiation therapy alone. Molecular markers were determined retrospectively. Survival and correlations were calculated using log-rank, univariate, and multivariate Cox proportional hazards-ratio analyses. All cases were isocitrate dehydrogenase 1 (IDH1) wildtype, MGMT promoter methylation could be observed in 33.3 % of the assessable cases (10/30) and TERT promoter mutation was seen in a high frequency of 86.7 % (26/30). The influence of TMZ therapy on overall survival (OS) was significantly improved compared with cases in which radiation therapy alone was performed (13.9 vs. 9.9 months; p = 0.045), independently of MGMT promoter methylation. The positive effect of TMZ on OS was confirmed in this study's multivariate analyses (p = 0.04), after adjusting our results for potential confounders. In conclusion, this study demonstrates that concomitant TMZ together with radiation therapy increases GSM-patient survival independent of MGMT promoter methylation. Thus, GSM can be treated in accordance to GBM guidelines. MGMT promoter methylation was infrequent and TERT promoter mutation common without influencing the survival rates. The mechanisms of TMZ effects in GSM are still not fully understood and merit further clinical and molecular-genetic and -biological evaluation.