Another study categorized PC by combining both the ISUP GGG system [45] and clinical staging (cT) (or TNM system) [48], classifying PC into the low aggressive group (GG 1 and stage cT1–cT2 and PSA < 10 ng/mL), aggressive group (GG 4 or 5, or PSA > 20 ng/mL, or GG 2-3 plus stage cT3-cT4) and intermediate aggressive group (all others) [37]. The gene discussed is KLK3; the disease is pachyonychia congenita.