The transmission of TGF-β signals begins with the binding of members of the TGF-β family to their specific receptors, including TGF-β receptor I (TβRI) and TGF-β receptor II (TβRII). These receptors are transmembrane serine/threonine kinases, and when TGF-β binds to these receptors, it promotes receptor dimerization and activation. The activated TβRII phosphorylates TβRI, which in turn activates its intrinsic kinase activity, phosphorylating downstream Smad proteins. The Smad complex acts as a transcription factor directly involved in the regulation of specific gene expression. In some types of cancer, the overactivation of TGF-β signaling promotes the invasiveness and metastatic capabilities of tumor cells. Conversely, in fibrotic diseases, the continuous activation of TGF-β leads to excessive deposition of extracellular matrix, affecting the normal function of tissues.