Association between a specific miRNA signature and pathological response to neoadjuvant chemoradiotherapy (CRT) in locally advanced rectal cancer (LARC) patients.

Abstract

e14057 Background: MicroRNAs (miRNA), small non-coding RNA molecules act as post-transcriptional regulators of gene expression and have shown diagnostic and prognostic potential in cancer. We profiled miRNA expression in LARC patients treated with neoadjuvant CRT to assess whether a miRNA signature correlated with the degree of pathological response. Methods: FFPE-derived tumour samples from 85 LARC patients treated with preoperative CRT (45 Gy plus 5.4 Gy boost, 180-cGy daily fractions and concurrent capecitabine) were analyzed for miRNA signature generation and IHQ-EGFR protein expression. Pathological response was scored according to the Mandard’s TRG scale. Expression profile of 667 mature miRNAs obtained by TLDA Human MicroRNA Panel or individual TaqMan MicroRNA Assays were normalized using RNU48, selected as the best normalizer by Normfinder program. The correlation between miRNA expression profile and pathologic response was assessed by class-comparison, unsupervised hierarchical cluster analysis and U-Mann Whitney test. Results: A pathological complete response was achieved in 12 patients (14%), whereas no response (TRG 3-4) was observed in 49 patients (58%). As expected, TRG correlated with both relapse and disease-free survival (p<0.01). We identified a miRNA signature that correctly differentiated extreme-phenotype of responder patients (TRG-1 vs TRG-4). The top 10 of them were selected to be validated by individual Q-RT-PCR in the global series. While up-regulation of miR-21*, miR-99*, miR-125b, miR-125b1*, let-7c and miR-490 significantly correlated with a higher likelihood of achieving pathological response (TRG-1-2), miR-21 and miR-125a-3p downregulated levels were found to be associated with a TRG-4 response. High EGFR protein expression levels, determined by IHQ, were seen in the 93% of poor-responders patients (TRG-4). Interestingly, miR-21 and miR-21* levels inversely correlated with EGFR expression. Conclusions: A differential expression of miRNAs may predict the degree of pathological response to CRT in LARC patients. A miRNA-mediated role for EGFR pathway in CRT resistance warrants further research.