Downregulation of miR-302b is associated with poor prognosis and tumor progression of breast cancer

Background MicroRNAs (miRNAs) are well known to play crucial role in various types of cancers, including breast cancer (BC). Methods The present study aimed to investigate the expression, clinical value, and functional role of miR-302b in BC. The expression level of miR-302b was determined by quantitative real-time polymerase chain reaction (qRT-PCR). The clinical value of miR-302b in BC prognosis was calculated via Kaplan-Meier survival analysis and Cox regression analysis. Cell experiments were applied to investigate the functional role of miR-302b in BC. Results miR-302b was significantly downregulated in BC tissues and cell lines compared to the corresponding controls (all P < 0.01). Notably, the expression of miR-302b was significantly associated with lymph node metastasis and TNM stage (all P < 0.05). Patients with lower miR-302b expression had shorter survival time than those with higher miR-302b expression (log-rank P = 0.002). Furthermore, miR-302b expression and TNM stage were proven to be independent prognostic factors for BC. Overexpression of miR-302b inhibited BC cell proliferation, migration, and invasion in BT549 and MCF-7 cell lines, while silence of miR-302b exhibited an opposite effects on BC cells (all P < 0.05). RUNX2 was determined to be the target gene of miR-302b. Conclusions The present study suggests that miR-302b functions as a tumor suppressor in BC and inhibits the tumor progression of BC via targeting RUNX2. Downregulation of miR-302b might be a significant prognostic factor for poor survival in BC patients.