Many studies show that deregulation of RSK proteins is associated with cancer development [45], but isoforms have opposite functions: RSK1 and RSK2 are considered as oncogenes, proved in many cancers (breast, lung, leukemia) including prostate, with RSK2-mediated increase in PSA expressions [46] compared with RSK3 and RSK4, but RSK3 activity has been studied only in ovarian and breast cancers [47, 48], and is unknown in prostate tumorigenesis. Here, RPS6KA2 is linked to breast cancer.