CD44 and prostate cancer: In human prostate cancer (PCa), several CSC populations have been reported using cell surface markers (for example, CD44, CD133, integrin α2β1, ABCG2 and so on), functional assays including side population and Aldefluor, and reporter-based lineage tracing strategies18, 19, 20, 21, 22, 23, 24, 25, 26.