A novel testis-specific gene expressed in human prostate cancer, designated 22P4F11, is described. Analysis of 22P4F11 mRNA expression in normal prostate, prostate tumor xenografts, and a variety of normal tissues indicates that the expression of this gene is testis specific in normal tissues. The 22P4F11 gene is also expressed in human prostate tumors, in some cases at high levels. A full length cDNA encoding 22P4F11 is provided. The 22P4F11 transcript and/or protein may represent a useful diagnostic marker and/or therapeutic target for prostate cancer.