The 4K score (OPKO Lab, Nashville, TN, USA) considers the serum levels of four kallikrein proteins, including PSA, free PSA, intact PSA and human kallikrein 2 (hK2), combining them with data from the digital rectal examination, age, and previous prostate biopsy, through an algorithm that therefore allows us to calculate the risk of high-grade PC [9]. Here, KLK3 is linked to pachyonychia congenita.