KISS1 (Metastasis-suppressor KiSS-1) is a metastasis suppressor protein found in malignant melanomas and in some breast cancers. KISS1 regulates events downstream of cell-matrix adhesion, perhaps involving cytoskeletal reorganization. KISS1 generates a C-terminally amidated peptide, metastin, which functions as the endogenous ligand of the G-protein coupled receptor GPR54. Activation of this receptor inhibits cell proliferation and cell migration, key characteristics of tumor metastasis. Kp-10 is a decapeptide derived from the primary translation product, isolated in conditioned medium of first trimester trophoblast. Kp-10, but not other kisspeptins, increased intracellular Ca2+ levels in isolated first trimester trophoblasts. Kp-10 is a paracrine/endocrine regulator in fine-tuning trophoblast invasion generated by the trophoblast itself. The receptor is also essential for normal gonadotropin-released hormone physiology and for puberty.