It has been reported that serum GGT activity was increased in certain types of cancer [22] and thus we measured serum GGT activity as well as serum exosomal GGT activity in patients with BPH (n = 8, PSA: 4.42–25.40 ng/mL) and PC patients (n = 31, PSA: 4.20–28.23 ng/mL). Here, KLK3 is linked to benign prostatic hyperplasia.