Functional studies based on cell lines experiments showed an implication of some of those miRNA in breast cancer; in particular, miR-532, miR-19b and miR-20b act as oncomirs by down-regulating the tumor suppressors RERG (ras-related and estrogen-regulated growth inhibitor), PTPRG (protein tyrosine phosphatase receptor type G) and PTEN (phosphatase and tensin homologue), respectively [48–50]; in contrast, miR-188 and miR-502 act as tumor suppressors by inhibiting TMED3 (Transmembrane Emp24 Protein Transport Domain Containing 3) and the H4K20 methyltransferase SET8, respectively [51, 52]. This evidence concerns the gene TMED3 and breast cancer.