Identifying the Primary Tumor Site and Distinguishing False-positives in Patients With Elevated Serum Carcinoembryonic Antigen.

BACKGROUND/AIM: Carcinoembryonic antigen (CEA) is a tumor marker that is frequently evaluated clinically for gastrointestinal and lung cancers. CEA is a glycoprotein antigen, and only the "value" measured by enzyme-linked immunosorbent assay is provided in the clinical setting. At present, no method has been established to indicate whether the value is a false-positive elevation or whether there is a primary cancer site. To obtain clues on how to identify the originating site in patients with cancer with high CEA levels and to identify CEA false-positives in healthy individuals, we conducted an exploratory study.

PATIENTS AND METHODS: A pilot study was performed using the multivariate analysis method and principal component analysis-discriminant analysis on proteomic results obtained using liquid chromatography-mass spectrometry (LC/MS) in two patients with lung cancer, one patient with gastric cancer, and one healthy control individual.

RESULTS: No differences in specific proteins associated with high CEA levels were detected between lung and gastric cancers using LC/MS. Therefore, we performed statistical analysis using principal component analysis-discriminant analysis to determine whether there were differences in the protein signal patterns obtained using LC/MS. The results showed that the plots obtained for each patient and the healthy control were located in different quadrants of the four-quadrant matrix scatter plot.

CONCLUSION: Our results suggest the possibility of visually differentiating the primary tumor site in patients with elevated CEA levels. This method may also help recognize false-positive CEA results.