Overexpression of miR-499a-5p in breast cancer cells promoted cell proliferation, upregulated the expression of oncogenes such as FOS, cyclin D3 (CCND3), and secreted phosphoprotein 1 (SPP1), and simultaneously downregulated tumor suppressor genes, including mouse double minute 2 (MDM2), von Hippel–Lindau (VHL), and polymerase beta (POLB). This evidence concerns the gene CCND3 and breast carcinoma.