Several studies have shown that miR‐215‐5p acts as a tumor suppressor in certain cancers, but its role in the progression and metastasis of breast carcinoma remains incompletely understood. Herein, we prove that miR‐215‐5p is substantially down‐expressed in breast carcinoma as compared with nontumor tissue. Up‐regulation of miR‐215‐5p inhibits the aggressive abilities of breast carcinoma cells in vitro. We performed luciferase reporter tests to show that SRY‐Box 9 (Sox9) is the target of miR‐215‐5p; as predicted, Sox9 depletion replicates the suppressive effects of miR‐215‐5p on breast carcinoma cells, and overexpression of Sox9 rescues the effects of miR‐215‐5p on breast cancer cell progression. In addition, a xenograft model assay was used to reveal that miR‐215‐5p inhibits breast cancer cell growth and metastatic potential in vivo. Overall, these results imply that miRNA‐215‐5p suppresses the aggressiveness of breast cancer cells through targeting Sox9.

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