Objective: Carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9) are the most common colorectal cancer markers. We aimed to identify the appropriate clinical conditions for measuring serum CEA and CA19-9 levels before surgery and during follow-up. Methods: This study included 1275 colorectal cancer patients who were divided into 3 groups according to preoperative CEA levels (group A, ≤5 ng/mL; group B, >5–≤11 ng/mL; group C, >11 ng/mL). Each group was subdivided into 2 groups according to preoperative CA19-9 levels (cutoff level: ≤37 U/mL). Recurrence and survival rates were analyzed. Results: Recurrence rate, disease-free survival after curative surgery, and prognosis were significantly worse in group A and B patients with high CA19-9 levels. At recurrence, CEA levels showed a greater increase in group B and C patients; CA19-9 levels increased in group A patients with high CA19-9 levels. At recurrence, high serum CA19-9 levels were observed in group A patients with high preoperative serum CA19-9 levels, even if the serum CEA level did not increase. Preoperative CA19-9 levels could predict recurrence and prognosis in groups A and B. Conclusion: Periodic CA19-9 determination is useful for monitoring recurrence among group A patients with high CA19-9 levels.
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