Purpose : We demonstrated that Hsa-miR-567 expression is significantly downregulated in poor prognosis breast cancer, compared to better prognosis breast cancer, having a role in the control of cell proliferation and migration by regulating KPNA4 gene. ; Methods and results : In this study, based on our previously published in silico results, we proved both in vitro (cell line studies) and ex vivo (clinical studies), that Hsa-miR-567 expression is significantly downregulated in breast cancer with poor prognosis when compared to breast cancer with better prognosis. More intriguingly, we demonstrated that the ectopic expression of Hsa-miR-567 in poor prognosis breast cancer cell line strongly inhibits in vitro cell proliferation and migration. Furthermore, we showed in vivo that breast cancer cells, stably expressing Hsa-miR-567, xenografted in mouse, reduce tumor growth ability. Consistently, we found that karyopherin 4 (KPNA4), predicted target gene of Hsa-miR-567 as identified by our in silico analysis, is upregulated in highly aggressive MDA-MB-231 breast cancer cell line and patient tissues with poor prognosis with respect to good prognosis. ; Conclusions : Our results suggest a potential role of Hsa-miR-567 as a novel prognostic biomarker for BC and as regulator of KPNA4.