Antiestrogen is a peptide competing with estrogens for binding to estrogen receptors. Antiestrogens are used in the treatment of breast cancers.Human: H-Cys-Asn-Val-Val-Pro-Leu-Tyr(PO3H2)-Asp-Leu-Leu-Leu-Glu-OH or H-CNVVPLY(PO3H2)DLLLE-OH