Serum GGT could be a specific biomarker reflecting the tumor GGT expression, given that most PC specimens (79%) showed moderate to strong GGT expression in the immunohistochemical analysis (Table 5) and that serum GGT could increase in patients with advanced cancer with GGT overexpression according to a recent systematic review [15]. This evidence concerns the gene GGT1 and pachyonychia congenita.