593381 Use of a metastin derivative for producing a prophylactic/therapeutic agent for androgen-independent cancer, wherein the metastin derivative is Ac-D-Tyr-D-Trp-Asn-Thr-Phe-AzaGly-Leu-Arg(Me)-Trp-NH2 (Compound No. 550) or Ac-D-Tyr-Hyp-Asn-Thr-Phe-AzaGly-Leu-Arg(Me)-Trp-NH2 (Compound No. 723), or a salt thereof. In particular the cancer is prostate cancer.