STAT3 and breast cancer: We also analyzed the levels of CDK5, p35, and STAT3 proteins in clinical samples and the results showed that CDK5 expression was positively correlated with STAT3 Ser-727 phosphorylation, which suggested that the phosphorylation of STAT3 plays an essential role in regulating prostate cancer progression and the Gleason score, in addition to similar findings of STAT3 in breast cancer [98].