Relationship Between CA 19.9 and the Lewis Phenotype: Options to Improve Diagnostic Efficiency

Background/Aim: Approximately 10% of patients are unable to synthesize CA 19.9 (Lewis-negative), and these results are erroneously considered false-negatives. The aim of this study was to confirm that CA 19.9 cannot be detected by immunoassays in Lewis-negative patients. Materials and Methods: CA 19.9 levels were measured by immunological assays and Lewis phenotype was determined by the haemagglutination reaction. Results: Patients with Lewis phenotype (a+b–) or (a–b+) had significantly higher CA 19.9 levels than Lewis-negative patients with active cancer (p<0.001), no-evidence of disease (NED) patients (p<0.001) or patients with benign disease (p<0.001). Ninenty-four percent of patients (33/35) with undetectable CA 19.9 had a Lewis-negative phenotype. Additionally, 94.7% (34/36) of patients with Lewis-negative phenotypes had undetectable CA 19.9 serum levels. Conclusion: Patients with undetectable CA 19.9 serum levels tend to be Lewis-negative, and CA 19.9 is not useful in diagnosis or follow-up.

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