In a series of reports by Wartenberg et al., P-glycoprotein expression in 3D multicellular PCa cultures has been associated with the appearance of quiescent cell areas in large tumor spheroids, whereas small, highly proliferative aggregates showed only weak expression of this protein and consequently do not exhibit an MDR phenotype [58,59,60,61]. Here, ABCB1 is linked to posterior cortical atrophy.