SMAD2 and breast carcinoma: At this time, TGF-β1 often promotes epithelial-mesenchymal transitions (EMT) in tumor cells, leading to tumor invasion and metastasis.[37] In most breast cancers and their metastases, the transformation of TGF-β1 from a tumor suppressor to a tumor promoter is positively correlated with phosphorylated Smad2/3.