Use of a steroid C17,20 lyase inhibitor, or a steroid C17,20 lyase inhibitor and a concomitant drug for the production of a drug for the prophylaxis or treatment of androgen-independent prostate cancer, wherein the steroid C17,20 lyase inhibitor is (+)-6-(7-hydroxy-6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-7-yl)-N-methyl-2-naphthamide or a salt thereof, and wherein the concomitant drug may be selected from the group consisting of a sex hormone drug, an alkylating drug, an antimetabolic drug, an anticancer antibiotic, vegetable alkaloid, an immunotherapeutic drug, a molecularly-targeted drug, and a pharmaceutical agent that inhibits the action of a cell growth factor or a receptor thereof, and wherein the preferred concomitant drug is a sex hormone drug selected from prednisolone and leuprorelin acetate.
