For instance, a test combining ctDNA with carcinoembryonic antigen (CEA) for colorectal cancer, and pancreatic carcinoma, ctDNA with prostate-specific antigen (PSA) for prostate cancer [14], and ctDNA with microsatellite alterations for lung cancer [16], could be a potentially useful tool for a better understanding of the disease progression and early-stage diagnosis. This evidence concerns the gene KLK3 and colorectal cancer.