and as Potential Signatures for Glioma Recurrence, Regardless of WHO Tumor Grade.

Background/aim: Micro RNAs (miRs; miRNAs) are small, non-coding RNA segments that influence gene expression. To do this, they bind to corresponding mRNA segments and inhibit the subsequent protein translation. Currently, about 200 transcripts are thought to be regulated by a single miRNA. Dysregulated miRNAs can act as tumor promoters as well as tumor suppressors. The aim of this study was to verify miR-LET-7a and miR-LET-7b as a signature for glioma recurrence detection by analyzing their expression in glioma tissue.

Materials And Methods: Only patients with two or more recurrences of glioma (n=25) were included in the study (tissue samples, n=89). Tissue was obtained during neurosurgical procedures and shock-frozen in liquid nitrogen. The patient cohort (female:male=12:13) had an average age of 35 years when first diagnosed (primary tumor: 13 WHO grade II, 7 WHO grade III and 5 WHO grade IV) and 48 years in the fifth relapse. Quantitative real-time polymerase chain reaction was performed to analyze miRNA expression. miR-151a-3p was used as an internal reference.

Results: Expression of miR-LET-7a and miR-LET-7b was significantly lower in the first recurrence than in the primary tumor. The expression of miR-LET-7a and -7b significantly decreased with increasing tumor grade. The strongest down-regulation was found between WHO grade III and IV. In paired samples in which tumor grade did not change between the primary and the first recurrence, the expression of both miRNAs remained significantly lower in the recurrent than in the primary tumor.

Conclusion: miR-LET-7a and miR-LET-7b represent a potential signature for glioma recurrence regardless of WHO grade.