KLK3 and prostate cancer: Finally, the accuracy with which CS prostate cancer within the PSA ‘grey zone’ is correctly identified or ruled out appears to be unsurpassed by other liquid biopsy biomarkers such as %fPSA [AUC 0.59 (95% CI, 0.53–0.65)], phi [AUC 0.64 (95% CI, 0.59–0.71)], %p2PSA [AUC 0.64 (95% CI, 0.58–0.70)] [27], and PCA3 [AUC 0.71 (95% CI, 0.61–0.81)] [28].