Furthermore, the decreased expression of several miRNAs (e.g., miR-335, miR-126, and miR-206) was detected in human breast cancer cells metastasizing to the bone, and the restoration of their expression prevented bone metastatic progression.318 MiR-135 and miR-203 have been reported to downregulate the expression of Runx2 in breast cancer cells, thus reducing metastasis formation in bone.319 MiRNAs do not always exert negative effects on bone metastases, and some of them act as onco-miRNAs. This evidence concerns the gene RUNX2 and breast cancer.