To address this question, we analyzed Mcl-1 and USP9x protein levels in human prostate samples classified by pathologists into benign prostatic tissue (Mcl-1: n = 7, USP9x: n = 18), low-grade prostate cancer (Gleason score 6–7, Mcl-1: n = 12, USP9x: n = 18), high-grade prostate cancer (Gleason score 8–10, Mcl-1: n = 14, USP9x: n = 17), and progressive prostate cancer of patients receiving palliative care to relieve pain (Mcl-1: n = 18, USP9x: n = 23). Here, MCL1 is linked to Familial prostate cancer.