The KISS1 gene produces a peptide product called kisspeptins (KP), which act as an endogenous ligand for a G-protein-coupled receptor, KISS1R (GPR54).84 KISS1 acts as a metastasis suppressor gene through its KP/KISS1R signalling in numerous human cancers (melanoma, pancreatic cancer and gastric carcinoma) by inhibiting cellular motility, proliferation, invasion, chemotaxis and metastasis.85 However, in breast cancer, KP stimulates invasion of cancer cells and high expression of KISS1; GPR54 mRNA levels positively correlated with shorter relapse-free survival. This evidence concerns the gene NPPA and breast cancer.