Carcinoembryonic Antigen (CEA): Origin, Role in Oncology, and Concentrations in Serum and Peritoneal Fluid.

CEA (carcinoembryonic antigen), which belongs to the acidic glycoproteins, is primarily produced during the fetal period. Following this stage, low levels of CEA are considered physiological, while elevated concentrations are associated with a range of both benign and malignant pathologies. The liver plays a key role in CEA metabolism. The most common material used to determine CEA concentrations by various techniques is blood, and measuring CEA in peritoneal fluid holds clinical value. CEA has been found to contribute to carcinogenesis, metastasis, and treatment resistance. Therefore, its serum concentration is widely used in oncology for prognosis, disease monitoring, and recurrence detection, despite its limited sensitivity and specificity, which prevent it from serving as a standalone diagnostic tool. Elevated serum CEA levels are linked to worse outcomes in lung, liver, breast, colorectal, and pancreatic cancers. Imaging and multi-marker panels that include CEA enhance diagnostic accuracy, but its role remains context-dependent and varies by cancer type. CEA levels in peritoneal fluid have been explored as a potential marker for detecting malignancy and predicting recurrence, particularly in gastric, gynecological, and colorectal cancers. Peritoneal fluid CEA has also been proven useful in differentiating the etiology of ascites. While cytology remains the standard for the detection of tumor cells in body fluids, its limited sensitivity provides a strong rationale for incorporating peritoneal fluid CEA measurements as a complementary diagnostic tool, potentially alongside other markers. Additionally, the lack of standardized measurement techniques and cut-off values underlines the methodological challenges that still need to be addressed in future research for both serum and peritoneal CEA levels.