TAC1 and breast cancer: SP belongs to tachykinins encoded by TAC-1, also known as pre-pro-tachykinin-A (Ppt-a) (54). Neurokinin receptor 1 (NK-1R), encoded by TACR1, is one of the families of G-protein coupled receptors (GPCR) combined with SP, which then promotes several signaling pathways for the progress of cancer (55)—for instance, SP, along with its high-affinity target NK-1R, was augmented and activated HER2 in breast cancer cell lines (HER2+) and primary cell culture from breast cancer patients (HER2+).