Purpose: Carcinoembryonic antigen is the classical tumor marker for colorectal cancer. The main clinical utility is in monitoring patients with colorectal cancer. Like carcinoembryonic antigen, the plasma level of CA 242 is elevated in patients with colorectal cancer. The purpose of this study was to investigate whether the plasma levels of carcinoembryonic antigen and/or CA 242 were elevated before clinical diagnosis of colorectal cancer.
Methods: The Northern Sweden Health and Disease Cohort was linked to the Swedish National and Regional Cancer registries, and 124 prospective cases with colorectal cancer were identified. Two referents for each case were randomly selected and matched for gender, age, date of sampling, and fasting time. Plasma from the included patients was analyzed for carcinoembryonic antigen and CA 242 using specific immunoassays.
Results: An elevated level of carcinoembryonic antigen before diagnosis was associated with an increased risk of developing manifest colorectal cancer (adjusted odds ratio, 7.9; 95 percent confidence interval, 2.1-29.1; P = 0.002). An elevated level of CA 242 was not significantly related to colorectal cancer risk. Elevated carcinoembryonic antigen levels were only seen in samples collected in the two-year time interval immediately before diagnosis. In this group, 30.4 percent of all plasma samples from cases were carcinoembryonic antigen-positive and 71.4 percent were future Dukes A or B cases. The specificity of the carcinoembryonic antigen test for identifying future colorectal cancer patients was 0.99 with a sensitivity of 0.12. For CA 242 the specificity was 0.92 and the sensitivity was 0.1.
Conclusions: Elevated carcinoembryonic antigen levels strongly indicate occult colorectal cancer. Although the specificity of the carcinoembryonic antigen test in its present form is high, the sensitivity is disappointingly low, prohibiting the use of the carcinoembryonic antigen test for mass screening.