ABCG2 and prostate cancer: Prostate cancer cell line 22RV1 expresses high surface levels of both CD117 and ABCG2 (CD117+ABCG2+ cells). This subpopulation shows hypomethylation in ABCG2 promoter and also overexpresses stem cells markers such as Nanog, Oct4, Sox2, Nestin, and CD133