--- - |2 Our results revealed that miR‐142‐3p could target Bach‐1in breast cancer cells leading to the reduction of EMT‐related proteins and reduced cell proliferation, invasion, and migration. The results also demonstrated that miR‐142‐3p could regulate important tumor suppressor miRNAs in breast cancer cells. The results suggest that miR‐142‐3p could be a good candidate for the targeted therapy of breast cancer, especially for the invasive type. Abstract Background Breast cancer is the most common type of cancer among women, and despite improved treatments, it remains a major challenge. However, improved mechanistic insight may lead to novel therapeutic strategies. miR‐142‐3p belongs to the miR‐142 family and is involved in pathogenesis and metastasis of various types of malignancies by targeting several important messenger RNAs (mRNAs) including Bach‐1. This is especially true for breast cancer, where Bach‐1 is involved in the metastatic spread by deregulation of metastasis‐associated genes. Methods In this study, we collected 24 breast cancer tissues with 24 adjusted normal tissues to measure the expression levels of miR‐142‐3p and Bach‐1 mRNA using quantitative reverse‐transcription polymerase chain reaction (qRT‐PCR) and IHC. miR‐142‐3p targeting of Bach‐1 expression in MCF‐7 and MDA‐MB‐468 breast cancer cells was evaluated using bioinformatics, qRT‐PCR and western blot analyses. The cellular proliferation, invasion, and migration were assessed by MTT, transwell matrigel and wound healing assay and the EMT‐associated proteins C‐X‐C chemokine receptor type 4 (CXCR‐4), matrix metalloproteinase‐9 (MMP9), and vascular endothelial growth factor receptor (VEGFR) were analyzed by western blot analysis. Also, the expression levels of tumor suppressors including miR‐330, miR‐145, and miR‐34a were estimated by qRT‐PCR. Results Analysis of paired specimens of primary malignant and normal tissues showed that miR‐142‐3p was downregulated, while Bach‐1 mRNA and protein both were overexpressed in the breast cancer tumors. This inverse relationship was confirmed by cell line experiments demonstrating that miR‐142‐3p expression reduced Bach‐1 mRNA levels. Furthermore, replacement of miR‐142‐3p could inhibit the proliferation, invasion, and migration in breast cancer potentially by targeting of Bach‐1 mRNA and subsequent inhibition of CXCR4, MMP9, and VEGFR protein expressions. In addition, induction of miR‐142‐3p could upregulate tumor suppressor miRNAs, including miR‐330, miR‐145, and miR34a. Conclusion For the first time, our results revealed that miR‐142‐3p could target Bach‐1in breast cancer cells leading to the reduction of EMT‐related proteins and reduced cell proliferation, invasion, and migration. The results also demonstrated that miR‐142‐3p could regulate important tumor suppressor miRNAs in breast cancer cells. In conclusion, our results suggest that miR‐142‐3p could be a good candidate for the targeted therapy of breast cancer, especially for the invasive type. - 'Journal of Cellular Physiology, EarlyView. '