For example, BRCA1 mutations are genetic markers for breast cancer risk (Miki et al. 1994), blood glucose is a standard chemical biomarker for monitoring diabetes, serum creatinine is a chemical marker for kidney function, and prostate specific antigen (PSA) is a protein biomarker for prostate cancer (Polascik et al. 1999). The gene discussed is KLK3; the disease is prostate carcinoma.