By determining ABCB1 promoter methylation and expression in 121 prostate cancers, 37 high-grade prostatic intraepithelial neoplasia, 26 benign prostatic hyperplasia, and ten morphologically normal prostate tissue samples, frequency and levels of ABCB1 promoter methylation increased from normal prostate tissue samples to high-grade prostatic intraepithelial neoplasia to prostate cancers [137]. Here, ABCB1 is linked to benign prostatic hyperplasia.