Estimating the probability of cancer with several tumor markers in patients with colorectal disease

Objective: The purpose of this study was to evaluate and compare serum tumor markers, carcinoembryonic antigen (CEA), CA 19-9, CA 242, CA 72-4 and hCGbeta, and their value in the diagnosis of malignant colorectal disease. Methods: The serum concentrations of the markers were measured in 204 patients with colorectal cancer and in 104 inpatients with benign colorectal disease. The combined use of the markers was evaluated with a logistic regression analysis. Results: When all five markers were evaluated in the same model, only CEA and CA 72-4 provided significant diagnostic information ( p < 0.001), indicating that their combination improves the accuracy. The probability of cancer for each patient was calculated entering CEA and CA 72-4 in the logistic regression model. Receiver-operating characteristic curves were constructed, and the difference in the area under the curve (AUC) values was determined between the markers and the calculated probability of cancer. Of the individual markers, the highest AUC was observed for CEA ( AUC = 0.746). The difference in the AUC between CEA and CA 72-4 (AUC = 0.716) was insignificant ( p = 0.492), but between CEA and the other three markers it was significant (p < 0.015). The calculated probability of cancer index, based on a combination of CEA and CA 72-4, had a significantly higher AUC ( AUC = 0.804) than CEA alone ( AUC = 0.746; p = 0.046). Conclusions: The diagnostic value of CA 72-4 was additive to that of CEA in colorectal cancer, and both markers contributed with significant diagnostic information. As a diagnostic test, the probability of cancer calculated with logistic regression provided higher accuracy than any of the markers alone, implying that it might be a useful diagnostic tool. Copyright (C) 2004 S. Karger AG, Basel.