TGFB1 and breast cancer: PCR analysis also verified that both TGF‐β1 and ZEB1 levels were significantly increased when the MCF7 cells overexpression of SIX‐1, whereas both TGF‐β1 and ZEB1 levels were significantly decreased when SIX‐1 was knocked down in MDA‐MB‐231 cells (Figure 4C,D), indicating that SIX‐1‐induced EMT in BC metastases may depend on TGF‐β1 and ZEB1.