The above studies suggest that in two undifferentiated prostate cancer cell models, small-sized cells possess higher CSC-associated properties (i.e., higher clonal, clonogenic, and tumorigenic capacities). Serial tumor transplantations are needed to verify the true CSC traits in small prostate cancer cells. Current experimental strategies in fractionating cancer cells into different sizes have obvious pros and cons. Nylon mesh-based size sieving represents a cheap and facile method that is gentle on cells leading to high viability; but purity is a concern and precise cell sizes cannot be determined. FACS produces populations with higher purity; however, the high speed at which cells are sorted leads to low cell viability. Also, the use of forward angle light scatter is not an accurate measure of cell size as light scatter is influenced by a number of factors. Finally, although FACS with beads sizing has been used to fractionate normal cells into cell populations of different sizes [32] and [46], our preliminary studies in PC3 cells, which vary widely in sizes in culture, demonstrate that this approach might not be readily applicable to cultured human cancer cells as two flow cytometers give completely different flow profiles (Figure 3F-G).