In the low p2PSA concentration range (0–20 pg/mL), aggressive forms of PC are correlated to elevated values of tPSA (10–20 ng/mL), sufficiently high values of fPSA (>2 ng/mL), and low values of PSA density (<0.3 ng/mL2). The gene discussed is KLK3; the disease is pachyonychia congenita.