Knockdown of LncRNA-HOTAIR suppressed the proliferation of MCF-7 cells. MCF-7 cells were transfected with lncRNA-HOTAIR siRNA and negative control siRNA for 72 h. (A) Levels of lncRNA-HOTAIR were assessed in the indicated cell lines via RT-qPCR. ##P<0.01 vs. the SKBR3 group; ***P<0.001 vs. the MCF-7 group. (B) Interference efficiency was also measured via RT-qPCR. ##P<0.01 and ###P<0.001 vs. the NC group. (C) MTT (*P<0.05 and **P<0.01 vs. the NC group; #P<0.05 vs. the control group) and (D) colony formation assays were performed to assess cell proliferation. The rate of colony formation was quantitatively analyzed. Magnification, ×100. **P<0.01 vs. the NC group; ##P<0.01 vs. the control group. Values are expressed as the mean ± standard deviation of three independent experiments. LncRNA, long non-coding RNA; HOTAIR, HOX transcript antisense RNA; RT-qPCR, reverse transcription-quantitative polymerase chain reaction; NC, negative control; siRNA, small interfering RNA; Dox, doxorubicin; OD, optical density.