miR‑30a inhibits epithelial‑mesenchymal transition and metastasis in triple‑negative breast cancer by targeting ROR1.

Triple‑negative breast cancer (TNBC) is a highly aggressive breast cancer subtype that lacks effective targeted therapies. In the present study, we revealed that the expression of miR‑30a was significantly decreased in TNBC, and TNBC patients with low expression of miR‑30a were associated with high histological grade and more lymph node metastasis. Moreover, we found that miR‑30a suppressed TNBC cell epithelial‑mesenchymal transition (EMT), as demonstrated by the overexpression of miR‑30a which increased the expression of epithelial marker E‑cadherin but decreased the expression of mesenchymal markers N‑cadherin and vimentin. Furthermore, we demonstrated that overexpression of miR‑30a significantly suppressed TNBC cell invasion and migration, as well as inhibited tumor growth and metastasis in vivo. More importantly, RTK‑like orphan receptor 1 (ROR1) was predicted as the direct target of miR‑30a, which was subsequently confirmed by luciferase assays. Forced expression of miR‑30a in TNBC cells decreased ROR1 expression, whereas the overexpression of ROR1 reversed the suppressive effects of miR‑30a in TNBC cell migration and invasion. Collectively, this study indicated that miR‑30a functions as a tumor‑metastasis suppressor miRNA in TNBC by directly targeting ROR1 and that miR‑30a may serve as a novel therapeutic target for TNBC.