A Combined Serum Biomarker Panel for Diagnostic and Prognostic Assessment in Esophageal Squamous Cell Carcinoma.

​Esophageal squamous cell carcinoma remains difficult to diagnose early and to stratify accurately before treatment. Conventional tumor-node-metastasis staging provides essential anatomical information but does not fully reflect circulating biological heterogeneity. This two-center ambispective observational study developed and externally validated a combined serum biomarker panel incorporating carcinoembryonic antigen, squamous cell carcinoma antigen, and carbohydrate antigen 125 for diagnostic discrimination and prognostic risk assessment in esophageal squamous cell carcinoma. A total of 277 participants were enrolled from a tertiary hospital and a community healthcare center, including 167 patients with esophageal squamous cell carcinoma, 55 patients with benign esophageal disease, and 55 healthy controls. The tertiary hospital cohort was used for model development and internal validation, and the community center cohort was used for external validation. Pretreatment serum biomarkers were measured before initial treatment, logarithmically transformed, standardized using training-cohort parameters, and entered into diagnostic logistic regression and prognostic Cox proportional hazards models. The combined panel showed higher diagnostic discrimination than any individual marker, with an area under the receiver operating characteristic curve of 0.869 in the training cohort and 0.842 in the external validation cohort. A higher combined biomarker burden was associated with tumor length of at least 5 cm, pT3-4 disease, lymph node metastasis, and tumor-node-metastasis stage III-IV disease. In survival analysis, high combined biomarker burden independently predicted poorer overall survival and progression-free survival after adjustment for major clinicopathological factors. The integrated prognostic model, combining biomarker burden with clinicopathological variables, outperformed the tumor-node-metastasis stage alone, with a training-cohort C-index of 0.792 and an external-validation C-index of 0.761. These findings support the use of the serum carcinoembryonic antigen, squamous cell carcinoma antigen, and carbohydrate antigen 125 panel as a practical, noninvasive adjunct for pretreatment assessment and individualized risk stratification in esophageal squamous cell carcinoma.