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BACKGROUND: (blind field). METHODS: RNA expression profiling was performed using DASL (Illumina) on 185 samples of which 113 were derived from BELOB trial samples and 72 were used to test the performance of the platform. RNA sequencing was performed on 96 samples, 78 of which were from BELOB trial samples. RESULTS: The DASL and RNA-seqs platform both show a high concordance between technical and biological replicates. Importantly, they also show a high concordance with expression profiling on snap frozen tissue samples and have a highly similar sample assignment to one of seven ‘intrinsic glioma subtypes’ (IGS; molecular subtypes of glioma based on similarities in gene-expression profiles [PMID: 19920198]). Most BELOB samples are assigned to poor prognostic subtypes (IGS-18 and IGS-23). However, four patients were assigned to prognostically more favourable subtypes (IGS-9 and IGS-17). EGFR mutations were identified by RNA-seq in the majority of IGS-18 samples (60%) but in only 17% of samples assigned to IGS-23. Multiple EGFR mutations in the same sample were frequently observed. IDH1 mutations were identified by RNA-seq in three samples. Correlation with clinical patient performance and treatment arm is ongoing. CONCLUSIONS: DASL and RNA-seq perform well on RNA isolated from FFPE tissues stored (up to 20 years) in paraffin. We are currently correlating the expression data with clinical data from the BELOB trial. SECONDARY CATEGORY: n/a.

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