In appropriate clinical context, the prostate-specific antigen (PSA) for prostate cancer, PAX8 for ovarian cancer, alphafetoprotein for liver cancer, and TTF1 for lung cancer can be reliably used as a single marker (Dennis et al. 2005; Rubin et al. 2001; Woodard et al. 2011). The gene discussed is KLK3; the disease is prostate cancer.