EZH2 expression in gliomas: Correlation with CDKN2A gene deletion/ p16 loss and MIB‐1 proliferation index

Enhancer of zeste homolog 2 (EZH2) mediated down‐regulation of CDKN2A/p16 has been observed in cell lines as well as in a few carcinomas. However, there is no study correlating EZH2 expression with CDKN2A/p16 status in gliomas. Hence, the present study was conducted to evaluate EZH2 expression in astrocytic and oligodendroglial tumors and correlate with CDKN2A/p16 status as well as MIB‐1 labeling index (LI). Gliomas of all grades (n = 118) were studied using immunohistochemistry to assess EZH2, p16 and MIB‐1 LI and fluorescence in situ hybrization to evaluate CDKN2A gene status. EZH2 expression and CDKN2A homozygous deletion (HD) were both significantly more frequent in high‐grade gliomas (HGG). Further, strong EZH2 expression (LI ≥ 25%) was significantly more common in HGGs without CDKN2A HD (48.7%; 19/39) as compared to cases with deletion (15.8%; 3/19). Loss of p16 expression was noted in 100% and 51.3% of CDKN2A deleted and non‐deleted tumors, respectively. Notably, 80% (16/20) of the CDKN2A non‐deleted HGGs with p16 loss had strong EZH2 expression, in contrast to only 15.8% (3/19) in the deleted group. Loss of p16 expression significantly correlated with MIB‐1 LI, irrespective of EZH2 status. Thus, this study shows that EZH2 expression correlates with tumor grade in both astrocytic and oligodendroglial tumors and hence can be used as a diagnostic marker to differentiate between low and HGGs. Further, this is the first report demonstrating an inverse correlation of strong EZH2 expression with CDKN2A HD in HGGs. Loss of p16 protein expression is mostly attributable to CDKN2A HD and correlates significantly with MIB‐1 LI. Notably, our study for the first time suggests a possible epigenetic mechanism of p16 loss in CDKN2A non‐deleted HGGs mediated by strong EZH2 expression. A hypothetical model for control of proliferative activity in low versus HGGs is therefore proposed.     

A comprehensive analysis identifies BRAF hotspot mutations associated with gliomas with peculiar epithelial morphology

Brain tumors harbor various BRAF alterations, the vast majority of which are the BRAF kinase‐activating V600E mutation. BRAF mutations are most frequently detected in certain subtypes of low‐grade glioma, such as pilocytic astrocytoma (PA), pleomorphic xanthoastrocytoma (PXA), ganglioglioma (GG) and dysembryoplastic neuroepithelial tumor (DNT). However, it is unclear whether gliomas harboring BRAF mutations can be invariably regarded as these glioma subtypes or their derivatives. To address this question, we analyzed 274 gliomas in our institutional case series. We performed high‐resolution melting analyses and subsequent direct Sanger sequencing on DNA isolated from snap‐frozen tumor tissues. As expected, BRAF mutations were detected in the aforementioned low‐grade gliomas: in 4/27 PAs, 2/3 PXAs, 4/8 GGs, and 1/6 DNTs. In addition to these gliomas, 1/2 astroblastomas (ABs) and 2/122 glioblastomas (GBs) harbored BRAF mutations. Pathological investigation of the two GBs revealed that one was a GB displaying epithelial features that presumably arose from a precedent GG, whereas the other GB, which harbored a rare G596 A mutation, showed marked epithelial features, including astroblastic rosettes. Our results indicate that in addition to being present in established BRAF‐associated gliomas, BRAF mutations might be associated with epithelial features in high‐grade gliomas, including sheet‐like arrangement of polygonal tumor cells with a plump cytoplasm and astroblastic rosettes, and thus could potentially serve as a genetic marker for these features.     

A proinvasive role for the Ca2+‐activated K+ channel KCa3.1 in malignant glioma

Glioblastoma multiforme are highly motile primary brain tumors. Diffuse tissue invasion hampers surgical resection leading to poor patient prognosis. Recent studies suggest that intracellular Ca²⁺ acts as a master regulator for cell motility and engages a number of downstream signals including Ca²⁺‐activated ion channels. Querying the REepository of Molecular BRAin Neoplasia DaTa (REMBRANDT), an annotated patient gene database maintained by the National Cancer Institute, we identified the intermediate conductance Ca²⁺‐activated K⁺ channels, KCa3.1, being overexpressed in 32% of glioma patients where protein expression significantly correlated with poor patient survival. To mechanistically link KCa3.1 expression to glioma invasion, we selected patient gliomas that, when propagated as xenolines in vivo, present with either high or low KCa3.1 expression. In addition, we generated U251 glioma cells that stably express an inducible knockdown shRNA to experimentally eliminate KCa3.1 expression. Subjecting these cells to a combination of in vitro and in situ invasion assays, we demonstrate that KCa3.1 expression significantly enhances glioma invasion and that either specific pharmacological inhibition with TRAM‐34 or elimination of the channel impairs invasion. Importantly, after intracranial implantation into SCID mice, ablation of KCa3.1 with inducible shRNA resulted in a significant reduction in tumor invasion into surrounding brain in vivo. These results show that KCa3.1 confers an invasive phenotype that significantly worsens a patient's outlook, and suggests that KCa3.1 represents a viable therapeutic target to reduce glioma invasion. GLIA 2014;62:971–981     

Cerebellar high‐grade astrocytoma with IDH mutations in the elderly: A report of two cases

Cerebellar high‐grade gliomas are rare, and likely to affect younger patients compared with those of cerebral origin. Recent genetic analyses have revealed that isocitrate dehydrogenase (IDH) 1/2 mutations are rare in infratentorial gliomas. In this paper, we report two elderly cases of IDH‐mutated cerebellar high‐grade glioma with unusual histological features and uncommon patient ages. One case was an 83‐year‐old man, whose tumor was predominantly composed of densely packed round‐to‐polygonal epithelioid cells. The other was a 75‐year‐old woman's high‐grade astrocytoma characterized by cord‐like structures and the perivascular papillary arrangements with varying amounts of myxoid matrix. The former harbored IDH1 R132H mutation, whereas the latter had IDH2 R172K mutation. According to our literature review, eight cases of IDH‐mutated infratentorial gliomas including the present cases have been reported, and four had mutations other than IDH1 R132H. Moreover, we herein report the first elderly case of IDH2‐mutation. Although the number is limited, IDH‐mutant infratentorial diffuse gliomas may have clinical, histological and genetic features different from supratentorial cases.     

The value and correlation between PRL‐3 expression and matrix metalloproteinase activity and expression in human gliomas

Local invasion of tumor cells is characteristic of most human glioma invasions. It is associated with increased motility and a potential to degrade the extracellular matrix. Matrix metalloproteinases (MMPs) have been proved to be a main process in local invasion of brain tumor. PRL‐3 is a new protein tyrosine phosphatase which would also degrade the extracellular matrix and has been proved to be expressed in liver metastases derived from colorectal cancer. In this study, we sought to investigate the expression of PRL‐3 in glioma tissues and investigate the relationship between MMPs (MMP2, MMP9, membrane‐type matrix metalloproteinase 1 [MT1‐MMP]) activity and expression in gliomas. The modifications of in situ hybridization of mRNA phosphatase of regenerating liver‐3 (PRL‐3) methods are preformed in the study of paraffin‐embedded slides. The immunohistochemistry and gelatin zymography are used to detect the expression of PRL‐3 and activity of MMPs. The results show that PRL‐3 mRNA and antibody of PRL‐3 are detected in glioma tissues mainly in grades IV and III, only a little in grade II, but not in normal brain tissue and glioma grade I. MMP2 and MMP9 are observed mainly in glioma tissues of grades IV and III in activity and expression. MT1‐MMP protein is located in glioma tissues and vessel endothelial cells. This is the first report of detecting PRL‐3 expression in gliomas, especially in grades III and IV, which may play an important role in progression of gliomas. PRL‐3, MMP2 and MT1‐MMP cooperatively contribute to gliomas invasion. Intermediate MMP2 (MT1‐MMP, TIMP‐2, MMP2 trimeric complex) is detected in high grades of glioma tissues by gelatin zymography and may be a marker indicating latent malignance of gliomas.     

Isocitrate dehydrogenase 1 and 2 mutations in gliomas

Over the past few years, new biomarkers have allowed a deeper insight into gliomagenesis and facilitated the identification of possible targets for glioma therapy. Isocitrate dehydrogenase (IDH) 1 and IDH2 mutations have been shown to be promising biomarkers for monitoring disease prognosis and predicting the response to treatment. This review summarizes recent findings in this field. Web of Science, Science Direct, and PubMed online databases were used to search for publications investigating the role of IDH in glioma. References were identified by searching for the keywords “IDH1 or IDH2 and glioma and diagnostic or predictive or prognostic” in papers published from January, 2008, to April, 2014. Only papers in English were reviewed. Publications available only as an abstract were not included. IDH1/2 mutations are tightly associated with grade II and III gliomas and secondary glioblastomas, with better prognosis and production of a recently described oncometabolite, 2‐hydroxyglutarate (2HG). Although the contradictory positive effect of IDH mutation on prognosis and negative role of 2HG in tumor transformation remain unresolved, the future direction of personalized treatment strategies targeted to glioma development is likely to focus on IDH1/2 mutations. © 2014 Wiley Periodicals, Inc.     

Disruption of transient receptor potential canonical channel 1 causes incomplete cytokinesis and slows the growth of human malignant gliomas

Despite decades of research, primary brain tumors, gliomas, lack effective treatment options and present a huge clinical challenge. Particularly, the most malignant subtype, Glioblastoma multiforme, proliferates extensively and cells often undergo incomplete cell divisions, resulting in multinucleated cells. We now present evidence that multinucleated glioma cells result from the functional loss of transient receptor potential canonical 1 (TRPC1) channels, plasma membrane proteins involved in agonist‐induced calcium entry and reloading of intracellular Ca²⁺ stores. Pharmacological inhibition or shRNA mediated suppression of TRPC1 causes loss of functional channels and store‐operated calcium entry in D54MG glioma cells. This is associated with reduced cell proliferation and, frequently, with incomplete cell division. The resulting multinucleated cells are reminiscent of those found in patient biopsies. In a flank tumor model, tumor size was significantly decreased when TRPC1 expression was disrupted using a doxycycline inducible shRNA knockdown approach. These results suggest that TRPC1 channels play an important role in glioma cell division most likely by regulating calcium signaling during cytokinesis. © 2010 Wiley‐Liss, Inc.     

Isolation of glioma cancer stem cells in relation to histological grades in glioma specimens

Purpose

The existence of cancer stem cells (CSCs) in glioblastoma has been proposed. However, the unknown knowledge that is yet to be revealed is the presence of glioma CSCs (gCSCs) in correlation to each WHO grades of glioma. We approached this study with a hypothesis that specimens from high-grade gliomas would have higher isolation rate of gCSCs in comparison to those of lower-grade gliomas.

Methods

The glioma specimens were obtained from patients and underwent gliomasphere assay. The gliomaspheres were chosen to be analyzed with immunocytochemisty for surface markers. Then the selected gliomaspheres were exposed to neural differentiation conditions. Lastly, we made mouse orthotopic glioma models to examine the capacity of gliomagenesis.

Results

The gliomaspheres were formed in WHO grade IV (13 of 21) and III (two of nine) gliomas. Among them, WHO grade IV (11 of 13) and III (two of two) gliomaspheres showed similar surface markers to gCSCs and were capable of neural differentiation. Lastly, among the chosen cells, 10 of 11 WHO grade IV and two of two WHO grade III gliomaspheres were capable of gliomagenesis. Thus, overall, the rates of existence of gCSCs were more prominent in high-grade gliomas: 47.6 % (10 of 21) in WHO grade IV gliomas and 22.2 % (two of nine) in WHO grade III gliomas, whereas WHO grade II and I gliomas showed virtually no gCSCs.

Conclusions

This trend of stage-by-stage increase of gCSCs in gliomas showed statistical significance by chi-square test linear-by-linear association. We prove that the rates of existence of gCSCs increase proportionally as the WHO grades of gliomas rise.     

脑胶质瘤EZH2基因的表达分析

目的探讨脑胶质瘤果蝇zeste基因增强子同源物2（EZH2）蛋白的表达变化。方法选取2010年5月至2011年12月手术切除的胶质瘤组织标本83例,其中2008年WHO分级Ⅰ级15例,Ⅱ级20,Ⅲ级26例,Ⅳ级22例;术前均未接受放疗或化疗。另外,收集30例颅脑损伤内减压手术切除的无肿瘤脑组织作为对照。采用实时荧光定量PCR法检测EZH2 m RNA表达。根据EZH2 m RNA表达水平分为高表达组（EZH2 m RNA≥0.3,48例）和低表达组（EZH2 m RNA〈0.3,35例）,分析两组术后生存期。结果胶质瘤组织EZH2 m RNA表达水平明显高于对照组（P〈0.01）,高级别胶质瘤（WHOⅢ、Ⅳ级）组织EZH2 m RNA表达水平明显高于低级别胶质瘤（WHOⅠ、Ⅱ级）组织（P〈0.01）。低表达组患者术后生存期较高表达组显著延长（P〈0.01）。结论脑胶质瘤组织EZH2 m RNA呈高表达,且其表达水平与病理分级具有相关性。     

IDH2 mutation in gliomas including novel mutation

Glioblastomas (GBMs) are the most aggressive type of primary brain tumors and provide a dismal prognosis. Thus far, several key genes have been identified in GBMs as prognostic and therapeutic targets. Mutations in two isocitrate dehydrogenase (IDH) genes, IDH1 and IDH2, commonly occur in low‐grade gliomas and secondary high‐grade gliomas, but are rare in primary GBMs. These mutations alter the catalytic activity of IDH proteins, promoting gliomagenesis. Gliomas with IDH1 or IDH2 mutation have better outcomes than do gliomas with wild‐type IDH. The hot spots of IDH1 mutations (R132) and IDH2 mutations (R140 and R172) are well known and are considered as a possible biochemical explanation for the differing clinical characteristics of primary and secondary GBMs. We sought to find the incidence of IDH2 mutation and the characteristics of the gliomas with IDH2 mutation. Among 134 gliomas, which were operated in our hospital consecutively, we studied IDH1 and IDH2 mutations by Sanger sequencing and IDH2 mutation was identified in seven cases (5.2%, four oligodendrogliomas and three GBMs). IDH2 mutation was found in 3.3% of GBMs (3/90 cases) and 9.0% (4/44) of grades II to III gliomas. Here, we report the clinicopathological characteristics of the gliomas with IDH2 mutations including two cases of primary GBM carrying a novel missense IDH2 mutation (c. 484C>T, p. P162S).     

Presence of pluripotent CD133+ cells correlates with malignancy of gliomas

BackgroundPresence of CD133⁺ cancer stem cells has been demonstrated within glioblastoma multiforme (GBM), the most malignant phenotype of gliomas (WHO grade IV). Since GBM frequently develops from low grade gliomas (WHO grade II) we assessed a possible qualitative or quantitative correlation of CD133⁺ cells and glioma grade to get new insights in gliomagenesis.ResultsThe amount of CD133⁺ cells within the bulk tumor mass, analyzed by immunostaining and Western blotting, showed a clear quantitative correlation with glioma grade (WHO° II, III and IV). Most of CD133⁺ cells were arranged in clusters frequently associated to tumor vessels. Protein analysis revealed high cellular coexpression of CD133 with Musashi-I but not CD34 indicating a neural, i.e. local origin of these cells. In vitro, no differences in stem cell properties concerning self-renewal and multi-lineage differentiation have been found for CD133⁺ cells isolated from gliomas of different grades.ConclusionsThese findings indicate a solely quantitative correlation of glioma grade with the presence of neural CD133⁺ cells within tumors supporting the concept of a CD133⁺ stem cell dependent gliomagenesis.     

Clinical presentation,immunohistochemistry and electron microscopy indicate neurofibromatosis type 2‐associated gliomas to be spinal ependymomas

Neurofibromatosis type 2 (NF2) is a hereditary tumor syndrome. The hallmark of NF2 is bilateral vestibular schwannoma. In addition, glioma is one of the diagnostic criteria of NF2. In this retrospective study the clinical presentation and histopathological features of 12 spinal gliomas from NF2 patients were assessed. Ten tumors were previously diagnosed as ependymomas and two as astrocytomas. However, upon re‐evaluation both astrocytomas expressed epithelial membrane antigen in a dot‐like fashion and in one case it was possible to perform electron microscopy revealing junctional complexes and cilia typical for ependymoma. The findings suggest that NF2‐associated spinal gliomas are ependymomas. Based on the fact that NF2‐associated gliomas are almost exclusively spinal and that no NF2 mutations have been found in sporadic cerebral gliomas, we suggest that “glioma” in the current diagnostic criteria for NF2 should be specified as “spinal ependymoma”.     

High expression of RFX4 is associated with tumor progression and poor prognosis in patients with glioblastoma

Abstract

Aim: Glioma stem cells (GSCs) have been shown to contribute to tumor development and recurrence, therapeutic resistance, and cellular heterogeneity of glioblastoma multiforme (GBM). Recently, it has been reported that GSCs lose their self-renewal ability and tumorigenic potential upon differentiation. In this study, we identified Regulatory Factor X4 (RFX4) gene to regulate GSCs’ survival and self-renewal activity in the GBM patients samples.

Materials and methods: We utilized public datasets from the Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), Ivy Glioblastoma Atlas Project, and The Human Protein Atlas to screen candidate genes which are associated with the development of GBM and poor patients survival. Small hairpin RNA (shRNA) lentivirus was applied to knockdown RFX4 gene in GSCs.

Results: We found that RFX4 mRNA expression among the RFX family was particularly reduced during GSC differentiation. RT-qPCR analysis revealed significant downregulation of RFX4 and stem cell markers (CD15 and CD133) mRNA expressions in primary human GBM-derived GSCs cultured under serum condition. Consistently, GSCs showed significantly elevated RFX4 mRNA expression levels compared to normal astrocytes, NHA, whereas glioma cells did not. Furthermore, analysis of the TCGA data set revealed that RFX4 is highly expressed in GBM, and contributes to the lowering of patient survival. Depletion of RFX4 using shRNA lentivirus in patient GBM-derived GSCs decreased neurosphere formation and cell viability.

Conclusion: These results suggest that RFX4 is a potential risk factor for maintaining the stemness of GSCs and making glioma more malignant, and thus, could be a promising target of GBM treatment.     

MS-275对原代培养的胶质瘤细胞及其干细胞生物学行为和耐药性的影响

目的 探讨组蛋白去乙酰化酶（HDAC）抑制剂MS-275对原代培养的胶质瘤细胞及其干细胞生物学行为和耐药性的影响。方法 取术中切除的脑胶质瘤瘤体深部无囊性变、无坏死肿瘤组织标本,分离获得胶质瘤细胞（GC）和胶质瘤干细胞（CSC）,细胞分为4组:GC组,CSC组,GC+MS-275组,CSC+MS-275组。GC组和CSC组不做药物处理;GC+MS-275组和CSC+MS-275组给予MS-275处理24 h（终浓度为8 mmol/L）。检测各组细胞HDAC水平;MMT法检测细胞增殖能力;免疫印迹法检测耐药信号通路相关蛋白（ABCG2、MPR1、MPR 4、Bax、Bcl-2、PI3K、p-PI3K）的表达;流式细胞仪检测细胞周期和细胞凋亡。结果 MS-275显著降低GC和GSC中HDAC水平（P<0.05）,显著抑制GC和GSC增殖能力（P<0.05）,显著增加G0/G1期细胞比例和细胞凋亡率（P<0.05）,显著增高GC和GSC中MPR4、ABCG2、MPR1、Bax、p-PI3K表达水平（P<0.05）,而显著降低Bcl2表达水平（P<0.05）。与GC+MS-275组比较,GSC+MS-275组变化更明显（P<0.05）。结论 MS-275促进GC和CSC凋亡,而且对CSC作用更强,其机制可能与PI3K/Akt信号通路有关     

The terminal prostaglandin synthases mPGES‐1, mPGES‐2, and cPGES are all overexpressed in human gliomas

Prostaglandin E2 has been connected to processes promoting tumor growth in several human malignancies including gliomas. The terminal prostaglandin synthases mPGES‐1, mPGES‐2, and cPGES convert PGH2 into prostaglandin E2. The inhibition of their function could significantly reduce PGE2 levels in tumors while avoiding some side effects related to the inhibition of the upstream enzymes COX‐1 and COX‐2. In this study, the immunohistochemical staining of mPGES‐1 and, for the first time, the staining of mPGES‐2 and cPGES are characterized and compared with COX‐1 and COX‐2 staining in the same tumor samples of 94 human gliomas. The main results demonstrate over‐expression of all three proteins, including cPGES and mPGES‐2 that are commonly considered non‐inducible, in both low‐ and high‐grade tumors. For all three proteins, average expression in tumor cells was higher in grade III tumors than grade II tumors. The analysis showed no correlation between tumor grade and staining of tumor cells or vascular endothelium with any of the antibodies except in oligodendrogliomas where moderate correlation (linear correlation coefficient 0.6; P < 0.01) could be found between tumor grade and tumor cell staining with mPGES‐1 and cPGES. In grade II tumors which recurred and were reoperated upon during the data gathering period, average expression of COX‐2, mPGES‐1, and cPGES was higher than in tumors that were operated on only once. Our results demonstrate the significance of all three terminal prostaglandin synthases, mPGES‐1, mPGES‐2, and cPGES, as a possible future target of inhibition in glioma therapy.     

TROP2 expression and its correlation with tumor proliferation and angiogenesis in human gliomas

Trophoblast cell surface antigen 2 (TROP2) is a transmembrane glycoprotein which is associated with tumor development and progression in a variety of epithelial carcinomas, while its expression and role in gliomas have not been considered. The aim of the study was to investigate TROP2 expression in malignant gliomas with different World Health Organization (WHO) classification and its correlation with tumor proliferation and angiogenesis. Immuohistochemistry was used to determine TROP2 and Ki-67 expression and microvessel density (MVD) in tumor specimens and normal brain tissues from 69 glioma patients and the relationship between TROP2 and Ki-67 and MVD was investigated. Immunohistochemistry results showed that the TROP2 expression was found in 59 (85.5 %) of the 69 tumor specimens, but no expression in normal brain tissues. Furthermore, TROP2 expression is significantly higher in WHO grade III (P = 0.025) and WHO grade IV (P = 0.011) gliomas than in WHO grade II gliomas. TROP2 expression correlates with Ki-67 (r = 0.676, P = 0.012) and MVD (r = 0.365, P = 0.035), but not with gender or age in human gliomas. These results suggested that the TROP2 correlated with malignancy, proliferation and angiogenesis in human gliomas. This is the first study describing TROP2 expression in gliomas and its proliferation and angiogenesis-related characteristic may serve as a potential therapeutic target for glioma treatment.     

Decreased expression of NDRG2 is related to poor overall survival in patients with glioma

Members of the NDRG (N-Myc downstream-regulated) gene family have been shown to play a variety of roles in human malignancies. In the present study, we examined the expression of NDRG2 protein in glioma samples of WHO grades I–IV. We also investigated the association between NDRG2 expression and survival. Immunohistochemical analysis was used to measure NDRG2 protein expression in 316 specimens of human glioma and 41 normal control tissues. Survival analysis was performed using the Kaplan–Meier method and Cox’s proportional hazards model. We found that NDRG2 expression was reduced in glioma relative to normal tissue, and that NDRG2 expression decreased with increasing glioma grade. Kaplan–Meier analysis showed that patients without NDRG2 expression had a lower survival rate than other patients. Multivariate analysis showed that NDRG2 expression was an independent prognostic factor for overall survival of patients with glioma. The present study provides the first evidence that NDRG2 expression is decreased in gliomas, indicating that NDRG2 may play an inhibitory role during the development of gliomas. NDRG2 expression may also be a significant and independent prognostic indicator for glioma.     

Stem cell protein BMI-1 is an independent marker for poor prognosis in oligodendroglial tumours

Aims: The polycomb factor BMI‐1 has recently been implicated in tumorigenesis of the central nervous system in several experimental animal models. However, the significance of BMI‐1 in human glioma has not been investigated. Here we describe expression of the polycomb protein BMI‐1 and its downstream targets p16^Ink4a and MDM2 in both high‐ and low‐grade human glioma. Methods: Tumour samples were collected from 305 adult patients treated for primary grades 2–4 gliomas between 1980 and 2006 in Finland and Germany. BMI‐1, p16 and MDM2 expression was evaluated using immunohistochemistry in representative paraffin‐embedded tumour tissue. The significance of observed immunoreactivity, age at onset, gender, histopathological findings and proliferative index was analysed in univariate and multivariate survival models. Results: BMI‐1 was expressed in all histologic types of diffuse gliomas. We found a significant correlation (P = 0.007) between the frequency of BMI‐1 immunoreactive tumour cells and poor survival in World Health Organization grades II–III oligodendrogliomas and oligoastrocytomas (n = 62). The median survival of patients grouped by low, intermediate or high frequency of BMI‐1 immunoreactive tumour cells was 191 months, 151 months and 68 months, respectively. This association was also significant in the Cox multivariate regression model. Nuclear p16 immunopositivity predicted better survival in astrocytomas and an inverse correlation between p16 expression and the Ki‐67 mitotic index was also observed. Conclusions: BMI‐1 is found in all histological types of gliomas and the relative protein expression of BMI‐1 is a novel independent prognostic marker in oligodendroglial tumours.