KISS1 and breast cancer: KPs (10, 13, 14 and 54 amino acids) are secreted, biologically active, blood-borne peptides, derived from a pro-peptide KISS1, that is cleaved rapidly by matrix metalloproteinases (MMPs), MT1-MMP1, MMP-9 and furin, to form KP-107, 10, 11, a highly studied peptide also produced by breast cancer cells12, 13, 14, 15, 16.