Multivariable Interaction Regression Model Adjusted Hazard Ratios (aHRs) for All-Cause Mortality (ACM) and Prostate Cancer–Specific Mortality (PCSM) for Each Clinical Factor Where a Persistent Prostate-Specific Antigen (PSA) at the First PSA Assessment Following Radical Prostatectomy (RP) Was Characterized as a Categorical or Continuous Covariate. This evidence concerns the gene KLK3 and prostate cancer.