KLK4 and prostate cancer: Even though diagnostic markers have found their niche in the clinical practice (selection of patients at risk of prostate cancer for biopsy based on serum (e.g. prostate-specific antigen, four kallikrein score) or urine analysis (RNA expression of PCA3 [9], or of gene pair HOXC6 / DLX1 [10]) [8], immunohistochemistry during primary diagnosis or metastatic disesase [11], theranostic targets for imaging, such as prostate-specific antigen [12]), prognostic biomarkers are still not recommended by professional guidelines, despite 40 years of intensive research in patients with prostate cancer.