CEACAM5 and neoplasm: While classical serum protein biomarkers (e.g., CA19-9 for diagnosis/monitoring, CEA for postoperative monitoring) are clinically established, non-protein biomarkers such as circulating tumor DNA (ctDNA) [79, 80] RNA signatures (e.g., miR-21) [81] metabolites [82, 83] and circulating tumor cells (CTCs) [84] show significant potential for early detection, prognostic evaluation, and treatment selection (Table 1).