Smad4 knockdown by shRNA or siRNA in breast cancer cells. (A) MDA-MB-231 with stable knockdown of Smad4 displays a reduced amount of invasion. A representative image from day 6, showing cells located in the collagen fibres of the tail is shown. (B) Transient knockdown of Smad4 in MDA-MB-231 cells was also capable of inhibiting the amount of invasion over 5 days. A representative image from day 5 is shown. Scale bar = 100 μm. Data are representative of three independent experiments with at least 50 embryos per group. Error bars represent standard deviation.