['We investigated the possible tumor suppressive effect of microRNA-107 (miR-107) in human breast cancer.', 'Gene expression of miR-107 in breast cancer cell lines and clinical breast tissues were evaluated by qRT-PCR. MiR-107 was stably overexpressed in MCF-7 and MDA-MB-231 cells through lentiviral transduction. Its role in regulating in vitro cancer proliferation, cell cycle, invasion and in vivo tumor growth was evaluated by MTT, flow-cytometry, transwell and in vivo tumorigenicity assays, respectively. Association of miR-107 and its downstream target, brain-derived neurotrophic factor (BDNF), was evaluated by luciferase assay and qRT-PCR. BDNF was further upregulated in miR-107-overexpressed MCF-7 and MDA-MB-231 cells to evaluate its role in regulating breast cancer in vitro proliferation, cell cycle and invasion.', 'MiR-107 was markedly downregulated in both breast cancer cell lines and breast tumors. MiR-107 overexpression markedly suppressed in vitro breast cancer proliferation, cell-cycle progression and invasion, as well as in vivo development of breast cancer xenograft. BDNF was proved to be the downstream target of miR-107 in breast cancer. BDNF upregulation functionally facilitated in vitro proliferation, cell-cycle progression and invasion in miR-107-overexpressed breast cancer cells.'] Is microRNA-107 downregulated and having tumor suppressive effect in breast cancer by negatively regulating BDNF?