Serum tumor markers are blood-based biomarkers that are potentially useful in cancer detection, surveillance following curative surgery, prediction of drug response or resistance, and monitoring therapy in advance setting.
International guidelines do not accept tumor markers in the process of gastric cancer (GC) diagnosis. Their usefulness in GC can be mainly acknowledged in monitoring the effectiveness of antineoplastic therapy and the surveillance period and in identifying patients at risk for GC. The majority of the commonly used tumor biomarkers are neither specific nor sensitive; moreover, the issue of the almost complete lack of prospectively validated data remains.
The four most frequently used tumor biomarkers in GC follow-up are carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA 19-9), carbohydrate antigen 125 (CA 125), and carbohydrate antigen 72-4 (CA 72-4). In particular, the value of pretreatment serum CEA also represents an independent prognostic factor; CA 19-9 value is often used for the diagnosis of GC; CA 72-4 is considered the major marker for GC, mainly for detecting advanced stages; and elevated serum CA 125 levels are associated with a variety of benign and malignant causes of pelvic mass, including peritoneal metastasis of GC.
Specific gastric biomarkers, i.e., pepsinogen (PG) I, PGII, gastrin-17 (G-17), and anti-Helicobacter pylori (HP) antibodies, are being used to identify patients at risk for development of GC, particularly combined in a panel test (GastroPanel) which provides comprehensive information on both the structure and the function of the entire stomach mucosa.
In the era of precision medicine, liquid biopsy may represent a prognostic or predictive biomarker and a noninvasive tool for monitoring disease in terms of evaluation of response to systemic therapy as well as in monitoring clonal evolution. It could also be useful for screening and earlier detection, but patients with early stage disease often harbor a plasma concentration of mutant template molecules which is beyond the limit of detection of the most diffuse technologies.
