MicroRNA in rectal cancer

Abstract

In rectal cancer, one of the most common cancers worldwide, the proper staging of the disease determines the subsequent therapy. For those with locally advanced rectal cancer, a neoadjuvant chemoradiotherapy (CRT) is recommended before any surgery. However, response to CRT ranges from complete response (responders) to complete resistance (non-responders). To date we are not able to separate in advance the first group from the second, due to the absence of a valid biomarker. Therefore all patients receive the same therapy regardless of whether they reap benefits. On the other hand almost all patients receive a surgical resection after the CRT, although a watch-and-wait procedure or an endoscopic resection might be sufficient for those who responded well to the CRT. Being highly conserved regulators of gene expression, microRNAs (miRNAs) seem to be promising candidates for biomarkers. Many studies have been analyzing the miRNAs expressed in rectal cancer tissue to determine a specific miRNA profile for the ailment. Unfortunately, there is only a small overlap of identified miRNAs between different studies, posing the question as to whether different methods or differences in tissue storage may contribute to that fact or if the results simply are not reproducible, due to unknown factors with undetected influences on miRNA expression. Other studies sought to find miRNAs which correlate to clinical parameters (tumor grade, nodal stage, metastasis, survival) and therapy response. Although several miRNAs seem to have an impact on the response to CRT or might predict nodal stage, there is still only little overlap between different studies. We here aimed to summarize the current literature on rectal cancer and miRNA expression with respect to the different relevant clinical parameters.

Keywords: Polymorphism; MicroRNA; Rectal cancer; Response; Chemoradiotherapy; Expression

Core tip: In rectal cancer, a proper staging of the disease determines the subsequent therapy. Also, prediction of prognosis or therapy response could serve to individualize therapy. MicroRNAs (miRNAs) are highly conserved regulators of gene expression, and seem to be promising candidates for biomarkers. Several miRNAs are part of a specific expression profile in rectal cancer tissue, while others have been correlated to clinical parameters and therapy response. However the comparison of different studies shows only little overlap and even partly oppositional results. Differences between analytical methods and tissue storage types can contribute to that. Further functional analyses are needed to fully understand the impact of miRNAs in rectal cancer.