ZC3H12D and breast neoplasm: Here, our findings demonstrate that RNA‐binding proteins (RBPs) ZC3H12D and DDX5 antagonize breast tumor cell cycle progression by competitively regulating the mRNA stability and expression of cell cycle‐promoting genes via targeting the RNA stem–loop structure, which broadens our understanding of the RBPs‐mediated post‐transcriptional regulation of cell cycle‐related genes.