Usefulness of the Serum Carcinoembryonic Antigen Kinetic for Chemotherapy Monitoring in Patients With Unresectable Metastasis of Colorectal Cancer

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Abstract
Purpose The aim of the study was to evaluate the relationship between serum carcinoembryonic antigen (CEA) kinetic and response to chemotherapy in patients with unresectable metastasis of colorectal cancer. Patients and Methods The kinetic was calculated using the slope of an exponential-regressive curve connecting the semi-logarithmic values of CEA. Receiver operating characteristic (ROC) curves were drawn to select the CEA slope thresholds to define patients with progressive or responsive disease with the highest sensitivity, specificity, and diagnosis accuracy odds ratio (DOR). The correlation between the CEA slopes and progression-free survival (PFS) was evaluated by the Cox model and Kaplan-Meier methods. Results A total of 122 patients were included. Progression defined by CEA slope greater than +0.05 resulted in sensitivity of 85.7%, specificity of 85.1%, and DOR of 34. The area under the ROC (AUROC) curve was 0.885 (95% CI, 0.815 to 0.936; P = .0001). Response defined by CEA slope less than −0.2 resulted in sensitivity of 74.7%, specificity of 82.5%, and DOR of 16. The AUROC curve was 0.847 (95% CI, 0.770 to 0.906; P = .0001). The difference between AUROC curves calculated with six or four CEA values was not significant. PFS was correlated with CEA slopes (hazard ratio, 4.6; 95% CI, 2.48 to 8.57). The median PFS was 10 months for patients with CEA slope values less than −0.2 months versus 6 months for patients with CEA slope values greater than −0.2 (P < .0001). Conclusion These results suggest that the CEA kinetic is an accurate, simple, and noninvasive method to identify the disease progression in patients with unresectable metastasis of colorectal cancer.