microRNA expression is able to predict response to chemoradiotherapy in rectal cancer.

Although global microRNA (miRNA) expression patterns of several embryologic, physiological and oncogenic processes have been thoroughly studied, no studies are available on the role of miRNAs in pre-operative chemoradiotherapy (CRT) in rectal cancer. This study aimed to delineate the expression pattern of miRNAs for the prediction of response to CRT in rectal cancer. Rectal cancer patients (n=43), who underwent pre-operative CRT (40 Gy radiotherapy combined with S-1), were studied. RNA harvested from rectal cancer biopsy specimens prior to pre-operative CRT was hybridized to miRNA microarrays (821 genes). The response to CRT was evaluated by histopathological examination of surgically resected specimens, Response Evaluation Criteria in Solid Tumors (RECIST) and downstaging. The data of miRNA microarray were evaluated by real-time reverse transcription-polymerase chain reaction (RT-PCR). Two miRNAs (miR-142-3p, 223) with an increased expression that correctly differentiated responders from non-responders to CRT were identified by histopathological examination. One gene (miR-223) showed a higher, while 8 genes (miR-20b, miR-92a, let-7a*, miR-20a, miR-17*, miR-106a, miR-17 and miR-20a*) a lower expression in responders compared to nonresponders, with regard to RECIST. The 3 genes (miR-223, miR-630 and miR-126*) had a higher expression in responders compared to non-responders, with regard to downstaging. The real-time RT-PCR evaluation analysis detected a higher miR-223 level in responders compared to non-responders. Consequently, candidate miR-223 may be a new biomarker for the prediction of response to CRT and may be useful when establishing tailor-made therapies for rectal cancer.