Contrary to our expectation, however, serum exosomal GGT activity exhibited no difference between PC patients with (n = 6, PSA: 7.46–585.70 ng/mL) and without (n = 35, PSA: 4.20–549.39 ng/mL) castration-resistance (Additional file 2: Fig. S1). This evidence concerns the gene KLK3 and pachyonychia congenita.