KLK3 and prostate cancer: Likewise, a prior study by Morris et al. reported low-grade fatigue as the most common toxicity among all three cohorts of patients (75 %; n = 3 [cohort 1], n = 3 [cohort 2] and n = 6 [cohort 3]) with progressive mCRPC (histologically confirmed prostate cancer, 25 % increase in PSA over three tests) following high-dose exogenous testosterone (transdermal; 5 mg; patch [cohorts 1 and 2] or gel [cohort 3]; 1 week, 4 weeks, or until progression for cohorts 1, 2 and 3, respectively) [109].