Negative Serum Carcinoembryonic Antigen has Insufficient Accuracy for Excluding Recurrence from Patients with Dukes C Colorectal Cancer: Analysis with Likelihood Ratio and Posttest Probability in a Follow-Up Study

This study was designed to determine the efficacy of carcinoembryonic antigen (CEA) monitoring for screening patients with colorectal cancer by using posttest probability of recurrence.For this study, 348 (preoperative serum CEA level elevated: CEA+, n = 119; or normal: CEA-, n = 229) patients who had undergone potentially curative surgery for colorectal cancer were enrolled. After five-year follow-up with measurements of serum CEA levels and imaging workup, posttest probabilities of recurrence were calculated.Recurrence was observed in 39 percent of CEA+ patients and 30 percent in CEA- patients, and CEA levels were elevated in 33.3 percent of CEA+ patients and 17.5 percent of CEA- patients. With obtained sensitivity (68.4 percent, CEA+; 41 percent, CEA-), specificity (83 percent, CEA+; 91 percent, CEA-) and likelihood ratio (test positive: 4.0, CEA+; 4.4, CEA-; and test negative: 0.38, CEA+; 0.66, CEA-), posttest probability given the presence of CEA elevation in the CEA+ and CEA- was 72.2 and 65.5 percent, respectively, and that given the absence of CEA elevation was 20 and 22.2 percent, respectively.Whereas postoperative CEA elevation indicates recurrence with high probability, a normal postoperative CEA is not useful for excluding the probability of recurrence.