RPS6KA3 and posterior cortical atrophy: Using an organoid model from PCa tumor tissue of Pb-Cre:Pten–/– mice, in which Rb is further knocked down by shRNA (Supplemental Figure 7H), we demonstrated that this organoid is not sensitive to palbociclib treatment, while RSK inhibition remarkably reduces the number and size of organoids (Figure 7, E and F).