KLK3 and pachyonychia congenita: Several forms of PSA, i.e., free PSA, or isoforms of PSA, i.e., -2 proPSA, have been evaluated alone or combined for PC screening, i.e., the prostate health index (PHI = (-2 proPSA/free PSA) x total PSA1/2) that improved the accuracy of PCa predictors at biopsy (16, 17).