KLK3 and breast cancer: Cancer biomarkers such as CEA56, AFP45, carbohydrate antigen 125 (CA125)40, prostate-specific antigen (PSA)57, carbohydrate antigen 72-4 (CA72-4)58, the extracellular domain of human epidermal growth factor receptor 2 (HER2-ECD)59, cytokeratin fragment antigen 21-1 (CYFRA21-1)60 and other proteins have been used for the detection, early screening, or prognosis assessment of many cancers, such as colorectal cancer, hepatocellular cancer (HCC), ovarian cancer, prostate cancer (PCa), gastric cancer, breast cancer, and non-small-cell lung cancer.