CEACAM5 and neoplasm: Conventional methods for monitoring PDAC, such as biopsies, are often invasive and pose risks to patients, while blood-based biomarkers like CA19-9 and carcinoembryonic antigen (CEA), although non-invasive, tend to be non-specific and may not fully capture the complex dynamics of the tumor microenvironment (TME), which is critical in determining immunotherapy outcomes [44,45,46].