ESR1 and breast cancer: There are indications that SERMs have an impact on cell‐extracellular matrix interaction which may subsequently affect invasiveness, for example, in breast cancer cells: Tamoxifen, a SERM, has been shown to reduce extracellular transforming growth factor‐beta 1 (TGF‐beta1) expression, while inhibition of matrix metalloproteinase (MMP) activity restored TGF‐beta1 levels in estrogen receptor‐positive breast cancer cells [9].