Through bioinformatic analysis and in vitro assays, we found that miR-29b expression was reduced by S100A7 in ER− MDA-MB-231 and increased by S100A7 in ER+ MCF7 cells, which at least partly explained the different roles of S100A7 in regulating proliferation of different types of breast cancer cells. Here, S100A7 is linked to breast cancer.