LAUSR

MiR‐21, the only microRNA (miRNA) found to be overexpressed in any type of solid tumor, its guide stand, miR‐21‐5p, has been studied a lot in colorectal cancer (CRC); however, few researchers focused on its passenger strand, miR‐21‐3p. In our study, based on The Cancer Genome Atlas (TCGA) data, we found that there were more varieties and quantities of miR‐21‐3p isoforms in microsatellite instability (MSI)‐type CRC. We further examined the role of miR‐21‐3p by in vitro and in vivo studies. MiR‐21‐3p may be an oncogene in CRC by promoting cellular mobility through epithelial–mesenchymal transition. However, different isoforms, especially miR‐21‐3p 0 | 2, may be a favorable prognostic marker for CRC survival, probably due to increased complementary effect of miR‐21‐5p and/or target genes. Further study investigating the underlying mechanism of miRNA isoforms is needed.