KLK3 and cancer: So far, the main cancer biomarkers that have been discovered include carcinoembryonic antigen (CEA), carbohydrate antigen 125 (CA125), carbohydrate antigen 15-3 (CA15-3), human epidermal growth factor receptor 2 (HER2), vascular endothelial growth factor 165 (VEGF165), tissue-specific antigen (TPS), prostate-specific antigen (PSA), alpha-fetoprotein (AFP), squamous cell carcinoma antigen (SCCA), circulating tumour cells (CTCs), microRNAs, and exosomes [7].