Neoadjuvant chemoradiotherapy (nCHT) followed by surgery is the mainstay treatment for locally advanced rectal cancer, leading to significant decrease in tumor size (downsizing) and a shift towards earlier disease stage in the primary tumor and lymph nodes (downstaging). Extensive histopathological work-up of the tumor specimen after surgery including tumor regression grading (TRG) and lymph node status (ypN) helped to visualize individual tumor sensitivity to CRT retrospectively. Since the response to nCHT is heterogeneous, however, valid biomarkers are needed to monitor tumor response. A relevant number of studies aimed to identify molecular markers retrieved from tumor tissue while the relevance of blood-based biomarkers is less stringent assessed. As a potential alternative to CEA and ctDNA, microRNAs (miRNAs) are currently under investigation to serve as blood-based biomarkers. miRNAs are small, noncoding RNAs that regulate gene expression by post-transcriptional mRNA binding, which promotes the destabilization of target miRNAs. The target specificity of miRNAs is largely predetermined by their so-called seed-sequence (containing nucleotides at position 2-7 of the miRNA). They are highly conserved between species, stable and easy detectable even in small concentrations. They have been widely analyzed in physiological and pathological processes, and their expression is tissue specific.