Abstract: An SLC18A2 gene serves as a marker of prostate cancer. Methods are provided for diagnosing prostate cancer, predicting or prognosticating the disease outcome, predicting recurrence following surgery, and monitoring disease progression in an individual having prostate cancer. The methods relate to determining the methylation state of an SLC18A2 gene and/or determining the level of transcription or translation of the gene in a sample from the individual. Methods of treating prostate cancer are also provided. The invention also pertains to compositions and kits for use in the methods.