[Commentary on] Highly purified CD44+ prostate cancer cells from xenograft human tumors are enriched in tumorigenic and metastatic progenitor cells. Patrawala L, Calhoun T, Schneider-Broussard R, Li H, Bhatia B, Tang S, Reilly JG, Chandra D, Zhou J, Claypool K, Coghlan L, Tang DG, Department of Carcinogenesis, The University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, TX.