The comparison of normal and tumor prostate samples revealed far more H3K27me3 marks in advanced tumor tissues compared to normal tissues. These alterations could have major impacts on global gene expression via chromatin state. Our observations suggested that H3K27me3 marks are active in tumor tissues. Increased H3K27me3 marks could be explained by the activity of the PcG such as EZH2, which is frequently over-expressed in prostate cancer [13, 33]. These results implied that the most numerous epigenetic changes from normal tissues to prostate cancer tissues were gains of H3K27me3 marks.