Smad3 mediates the functions of the TGF‐β pathway by interacting with various cofactors, and these R‐Smad binding partners include transcription factors from the forkhead, homeobox, bHL and AP1 families.[27] However, the Smad3 cofactors involved in lung metastasis in breast cancer are still poorly understood. This evidence concerns the gene SMAD3 and breast cancer.