A peptide vaccine derived from the synthetic peptide pyroEHWSYGLRPG, corresponding to amino acids 22-31 of mouse gonadotropin releasing hormone (GnRH), with potential immunocastration activity. PEP223 is dimerized and contains a D-lysine (k) substitution at position 6 (pyroEHWSYkLRPG) to increase its immunogenicity. Anti-GnRH vaccine PEP223 may stimulate the immune system to mount a cytotoxic T-lymphocyte (CTL) response against GnRH, neutralizing its activity. In turn, testosterone production and tumor cell growth may be inhibited in testosterone-sensitive tumors. Check for active clinical trialsusing this agent.