Recurrent FGFR1 amplification and high FGFR1 protein expression in oral squamous cell carcinoma (OSCC)☆
Introduction
Oral squamous cell carcinoma (OSCC) belongs to the 10 most common human malignancies worldwide affecting more than 500,000 individuals per year.1 Local aggressiveness, high rate of early relapse tumours and reduced 5-year survival rates not exceeding 50% are typical clinical features of this neoplasm. During the last decade, genome screening approaches like chromosomal comparative genomic hybridisation (CGH) were applied to disclose the molecular basis of oral carcinogenesis. This revealed frequent copy numbers gains of chromosomal arms 8q, 9q, 11q, 17q and 20q as well as losses of 3p, 4q, 9p and 18q, which were associated with initiation and progression of oral cancer.2 However, since the resolution of chromosomal CGH is rather low (∼5 Mb)3 it was not possible to pinpoint individual candidate genes potentially contributing to OSCC pathogenesis within these regions.
Matrix-CGH4 represents a DNA array based approach, which allows a comprehensive detection of copy number gains and losses with much higher resolution than chromosomal CGH (∼50 kb).5 The potential of this approach has been previously demonstrated in various tumour systems.6 Combing matrix-CGH with high throughput tumour analysis using tissue microarray technology (TMA) allows to rapidly assessing the overall prevalence of candidate oncogenes in representative tumour series. Furthermore, correlation of the results from TMA analyses with clinical parameter allows the elucidation of the diagnostic and prognostic potential of the corresponding genes and proteins.7, 8
Recently, a DNA array constructed for matrix-CGH experiments was presented by our group, which contained 812 different BAC clones representing known oncogenes (OG), tumour suppressor genes (TSG) as well as genomic regions, which were frequently found altered in different tumour types but where the target genes are still unknown. This DNA array was validated on a large collection of B-cell chronic lymphatic leukemia (B-CLL) and pancreatic carcinoma specimens by identifying recurrent genomic aberrations at high resolution.9, 10 In the present study, this DNA array was applied for the genomic profiling of 12 primary OSCC. Among others, a novel distinct high-level amplification of the gene FGFR1 was detected in two cases. Subsequent FISH and IHC analysis on TMA sections of a clinically well-defined representative OSCC collection was performed to enlighten the possible role of FGFR1 amplification and FGFR1 protein expression in the clinical course of oral carcinogenesis.
Section snippets
OSCC
Twelve tumour samples were collected from patients with histological confirmed primary OSCC prior to therapy after approval by the Institutional Medical Ethics Commission and informed consent. All except one OSCC were stage IV tumours (OSCC 11, stage II) according to the UICC grading system. Hematoxylin/eosin (H& E) staining was used in order to ensure that the selected tumour sample contained more than 70% tumour cells.
Matrix-CGH
The DNA chip used for this study was described previously.10, 11 Briefly,
Matrix-CGH
Analysis of 12 OSCC revealed imbalances of 66 genomic regions i.e. 29 copy number losses, 30 low copy number gains and 7 high-level amplifications. Chromosomal regions as well as the corresponding candidate genes most frequently affected by copy number gains were 3q27 (PIK3CA, BCL6; 7 cases), 7p12 (EGFR; 7 cases), 8q24 (MYC; 7 cases) and 11q13 (CCND1; 4 cases). Copy number losses were mostly found on 1p (4 cases), 8p23 (TRAIL1; 4 cases) and 11q23 (ATM; 3 cases). All global chromosomal
Discussion
In the present study, we combined the approach of matrix-CGH and TMA analysis. This allows an effective genomic screening and the identification of chromosomal copy number changes at high-resolution (∼50 kb). In this experimental setting, an immediate testing of the impact of the affected gene loci on tumour development as well as on clinical parameters in large collections of selected tumour cases can be performed.
Applying matrix-CGH for the analysis of 12 OSCCs revealed a number of chromosomal
Acknowledgement
We thank Stefanie Hofmann, Frauke Devens and Laura Puccio for their technical assistance.
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Cited by (0)
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Supported in part by the National Genome Research Network (NGFN2/No. 01 GR 0417), the Tumorzentrum Heidelberg/Mannheim (FSPI.-4.) and the medical faculty of the University Heidelberg.
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Both authors contributed equally to this work.