Analysis of certain circulating biomarkers has already yielded important prognostic and diagnostic information, such as prostate-specific antigen (PSA) in prostate cancer [10] and carcinoembryonic antigen (CEA) in colorectal cancer [11], while others have assisted assessment of treatment response and resistance, including circulating tumor DNA (ctDNA) [12, 13] and cancer antigen CA125 [14]. The gene discussed is CEACAM5; the disease is colorectal cancer.