KLK3 and pancreatic ductal adenocarcinoma: Several long-used cancer diagnostic biomarkers include prostate-specific antigen (PSA), used for diagnosis of prostate cancer (Welch and Albertsen 2009); cancer antigen 19-9 (CA 19-9), the gold standard serum biomarker for diagnosis of pancreatic ductal adenocarcinoma (PDAC) (Poruk et al., 2013); and CA 125, a classical biomarker in ovarian cancer (Felder et al., 2014).