KLK3 and gastric cancer: However, breast cancer screening technology (mammography, ultrasound, and magnetic resonance imaging), prostate cancer marker detection (prostate-specific antigen, PSA), and hepatocellular carcinoma marker detection (alpha-fetoprotein, AFP) suffer from high false positive rates and limited sensitivity [10,11,12], and gastric cancer detection technology (gastroscopy) has poor patient compliance, which is not enough to solve clinical difficulties.