Abstract Prostate cancer is the most commonly diagnosed malignancy and the second leading cause of cancer death among men in the United States, with an estimated 220,800 new cases and 27,540 deaths in 2015. Epidemiological studies have shown that dietary compounds have significant effects on prostate carcinogenesis. Among dietary agents, genistein, the major isoflavone in soybean, is of particular interest because high consumption of soy products has been associated with a low incidence of prostate cancer, suggesting a preventive role of genistein in prostate cancer. In spite of numerous studies to understand the effects of genistein on prostate cancer, the mechanisms of action have not been fully elucidated. Here, we investigated the differences in methylation and gene expression levels of prostate specimens from a clinical trial of genistein supplementation prior to prostatectomy (Lazarevic B, et al. Nutr Cancer 2011). This study was a randomized, placebo-controlled, double-blind clinical trial on forty-seven Norwegian patients who received 30 mg genistein or placebo capsules daily for 3-6 weeks before prostatectomy. Whole genome methylation and expression profiling identified significantly differentially methylated sites and expressed sites between placebo and genistein groups. Differentially regulated genes were involved in developmental processes, stem cell markers, proliferation, and transcriptional regulation. These findings highlight the effects of genistein on global changes in DNA methylation and gene expression in prostate cancer, and provide additional insight into the multiple molecular pathways involved in prostate tumorigenesis. Citation Format: Birdal Bilir, Jeongseok Edward Lee, Nitya V. Sharma, Bato Lazarevic, Aud Svindland, Omer Kucuk, Carlos S. Moreno. Effects of genistein supplementation on genome-wide DNA methylation and gene expression in patients with localized prostate cancer. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Sep 24-27, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2016;76(2 Suppl):Abstract nr A46.