CD44 and posterior cortical atrophy: A very small proportion of cells that are CD44+/α2β1/CD133+ and do not express AR, comprising less than 0.1 percent of the tumor volume, have been identified as prostate cancer stem cells (PCSC) [34,35]; the hierarchy stem cell model of PCa states that only this small subset of cells is responsible for the androgen-independent cell growth seen in PCa [35,36].