Although the source of serum GGT in men with mCRPC is largely unknown, it could be derived from PC cells, given that higher immunopositivity of GGT was observed in prostatic adenocarcinomas than in normal prostatic cells based on previous immunohistochemical analysis [16], and that cultured PC cells released soluble GGT complexes into supernatants [17]. Here, GGT1 is linked to prostate adenocarcinoma.