KLK3 and prostate carcinoma: For example, in the USA screening for prostate cancer in men over 50 years of age now consists of a digital rectal exam (DRE; a physical marker) and a PSA (prostate-specific antigen) test in serum (a biochemical marker), that together have a substantially higher detection rate than does either marker alone (Catalona et al 1994; Schröder et al 1998; Schröder et al 2001; Vis et al 2001).