TAC1 and breast cancer: The most important findings of this study were the following: BC cells express mRNA for neurokinin receptor 1; this receptor is overexpressed in BC cells; neurokinin receptor 1 mediates the viability of BC cells; substance P promotes the proliferation of BC cells; neurokinin receptor 1 antagonists, via neurokinin receptor 1, block the mitogenesis of BC cells mediated by substance P, and neurokinin receptor 1 antagonists promote the death of BC cells by apoptotic mechanisms [228].