Original articleCytogenetic and molecular genetic analyses of giant cell glioblastoma multiforme reveal distinct profiles in giant cell and non-giant cell subpopulations
Introduction
Giant cell glioblastoma (gcGBM) is a peculiar variant of glioblastoma multiforme (GBM) that accounts for up to 5% of cases [1]. Compared with classic glioblastoma, it shows clinicopathological and genetic differences. Notably, it develops in patients with a short disease history and appears to be associated with a better outcome than classic GBM [2], [3].
The pathological analysis of gcGBM shows typically a strong preponderance of large multinucleated polymorphic giant cells and, in a fraction of cases, an abundant stromal reticulin network [2]. Classic GBM may develop from a preexisting low-grade astrocytoma or evolve de novo. Most of the de novo glioblastomas usually carry an amplification of the epidermal growth factor receptor (EGFR) oncogene without TP53 mutations; this is termed type 2 GBM [4]. In contrast, type 1 GBM frequently harbors TP53 inactivation without EGFR amplification [2], [4]. Less information is available for gcGBM, which, like type 2 GBM, clinically arises de novo. Molecular alterations appear to occupy a position intermediate to those observed in GBM types 1 and 2.
The gcGBM are similar to type 1 GBM in that they have TP53 mutations and lack EGFR amplification and are similar to type 2 GBM (in addition to de novo appearance) in having a comparable mutation frequency for PTEN [phosphatase and tensin homolog (mutated in multiple advanced cancers 1); alias MMAC1]. However, the pattern of TP53 mutations differs in gcGBM from that in type 1 GBM, and, in contrast to type 2 GBM, gcGBM have a near absence of CDK4 amplification and CDKN2A homozygous deletion [5], [6].
Little is known with regard to cytogenetic aberrations in gcGBM. In two previous studies, few chromosomal imbalances were observed with comparative genomic hybridization (CGH) analysis [3], [7]. A low incidence of chromosomal aberrations has been reported in tumors with microsatellite instability (MSI), another form of genomic instability [8], [9], [10], [11]. MSI is a consequence of inactivation of mismatch repair (MMR) genes involved in correcting DNA mismatches [12]. Inactivating mutations of MMR genes highly increase the occurrence of alterations in both coding and noncoding regions in other genes, such as PTEN (alias MMAC1) [13], TGFBR2 (transforming growth factor beta receptor II [14]), BAX (BCL2-associated X protein [15]), APC (adenomatous polyposis coli [16]), or IGF2R (insulin-like growth factor type 2 receptor [17]).
Because molecular differences have been observed between classic GBM and gcGBM [2], [5], [6], we wondered whether these could be explained on the basis of distinct profiles of genomic instability, at both the chromosomal and the microsatellite level. For this purpose, we investigated in both classic GBM and gcGBM the pattern of microsatellite instability, the expression of four major MMR proteins, TP53 mutation status, and EGFR oncogene copy number. Moreover, to assess chromosomal instability, numerical changes of five selected chromosomes were investigated with FISH in both classic GBM and gcGBM; giant cell and nongiant cell phenotypes of gcGBM were analyzed separately.
Section snippets
Tumor samples
Twelve tumor samples of gcGBM were obtained from 10 patients who were surgically treated at the University Hospitals of Dresden and Würzburg, Germany (Table 1). Furthermore, tumor samples from 12 consecutive classic GBM patients were analyzed for comparison. An informed consent from each patient or patient's caretaker was obtained. For gcGBM, we considered only typical cases with predominance of giant multinucleated glial fibrillary acidic protein (GFAP)–positive tumor cells; glioblastomas
Clinicopathological characteristics
The ratio of males to females among the gcGBM patients was 1:2, and the median age was 52 years (range, 44–69 years; standard deviation, 7.7). The sex ratio and median age of the classic GBM group did not differ significantly from the gcGBM group (both P > 0.05, chi-square test).
Histological and immunohistochemical analyses of classic GBM revealed the typical characteristics of these tumors and will not be described in detail. In gcGBM, routine hematoxylin–eosin-stained sections demonstrated a
Discussion
The present study revealed clear differences in genetic instability mechanisms between gcGBM and classic GBM. In a recent study, we found MSI in 7.8% of 128 classic GBM, affecting only di- and tetranucleotides and showing positive expression of MMR proteins [26]. In gcGBM, we have now observed a higher MSI rate (30%, P = 0.054, two-tailed Fisher exact test), as well as a different pattern of MSI, with instability affecting mono- and dinucleotide repeats. MSI could not, however, be explained in
Acknowledgments
This work was supported by a grant from the Deutsche Forschungsgemeinschaft, DFG (MA 2448/1) and the National Genome Research Network (NGFN2/No. 01 GR 0417). We thank Prof. Dr. med. K. Roosen (Director of the Department of Neurosurgery, University of Würzburg, Germany) for kindly providing gcGBM tumor samples. We also thank Frank Gottron, PhD, for helpful discussion and Mrs. F. Devens, German Cancer Research Center (DKFZ), Heidelberg, and Mrs. M. Reichman, Department of Surgical Research,
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Present address: Department of Neurosurgery, Klinikum Fulda, Academic Hospital, Philipps University Marburg, Pacelliallee 4, D-36043 Fulda, Germany.