Fosfestrol (INN, BAN, JAN) (brand names Honvan, Difostilben, Fosfostilben, Fostrolin, Stilbol, Stilphostrol, Vagestrol, among others), also known as diethylstilbestrol diphosphate (USAN), abbreviated as DESDP or DESP, is a synthetic, non-steroidal estrogen of the stilbestrol group that is or has been used in the treatment of prostate cancer.