Micro-RNAs as positive biomarkers of pathological complete response after neoadjuvant chemoradiotherapy in locally advanced rectal carcinoma.

Abstract

624 Background: Neoadjuvant chemoradiotherapy (nCRT) follow by surgery, as treatment for locally advanced rectal carcinoma (LARC), has improve local disease control, increase of complete pathological response (cPR) and preserve anal sphincter. cPR is associated with better prognosis. CRT act mainly through induction of DNA damage. MicroRNAs (miRNAs) are small non-coding RNAs able to regulate gene expression at post-transcriptional level. miRNAs are involved in the regulation of DNA damage/repair mechanism. Our goal was to measure expression of miRNAs involved in DNA damage/repair genes and correlated with cPR. Methods: Retrospectively, we analyzed the initial paraffin embedded tissue block of 20 Mexican patients with LARC treated with nCRT at National Cancer Institute of Mexico between 2010-2013. Treatment response was evaluated with Ryan Classification. Ten patients had cPR (Ryan Grade 0) meanwhile other 10 poor response (Ryan Grade 3). RNA extraction was done with RNeasy FFPE (Qiagen) Kit. RNA concentration and purity was assessed using NanoDrop 2000 Spectrophotometer. miRNAs expression were evaluated by real-time polymerase chain reaction (PCR) analysis with TaqMan Probes from Applied Biosystems. Statistical analysis was carried out with IBM SPSS Statistics 22.0. Differential expression between the two groups was performed with Chi square test. Results: There wasn’tsignificant difference betweenclinical/demographic features between the 2 groups. All patients received CRT at a total dose of 4500 cGy of pelvic irradiation, concomitantly with fluoropyrimidine. Surgical treatment was performed 14 weeks after completion of nCRT. The 2 miRNAs (188-5p and 590-5p) was overexpressed in the cPR group vs poor response group (p = 0.011 and p = 0.057, respectively). Conclusions: We evaluated the expression of miR590-5p and miR188-5p because they are related to DNA repair genes such as: MSH2, ERCC3, BRCC3 and XRCC5. We found overexpression in both miRNAs. Even though miR590 5p didn't reach statistical significance this maybe because of simple size.Our results now are been analyzed with a biological and functional genes network platform: Ingenuity Pathway Analysis.