SMAD3 and neoplasm: TGF‐β is known to regulate the expression of MMPs via Smad and non‐Smad pathways in tumor stromal cells (Krstic & Santibanez, 2014); TGF‐β and p‐Smad3 were also elevated in syncytiotrophoblast on day 5 (Fig 4G and H), suggesting that they play a role in regulation of MMP expression in the placenta.