Investigation of unexpected serum CA19-9 elevation in Lewis-negative cancer patients

Abstract

Background Cancer patients with a Lewis (a−b−) phenotype have no carbohydrate antigen 19-9 (CA19-9) in their serum. However, we found a small but distinct elevation in the serum CA19-9 level in three cancer patients with the Lewis-negative phenotype. Here, we investigated the reason of such phenomena. Methods Six cancer patients with a Lewis-negative phenotype were selected by very low CA19-9 concentrations: three showed a small elevation (Group A) and the other three showed no elevation (Group B) in the serum CA19-9. We investigated the difference by analyzing the Lewis/Secretor genotypes. Results All of the six patients with a Le (a−b−) phenotype were genuine Le-negative genotypes: four individuals were homozygous for le1 ( le59,508), one patient was compound heterozygous for le1 ( le59,508) and le2 ( le59,1067) and one patient was compound heterozygous for le1 and le202,314. As for the Secretor gene, the three patients in Group B were homozygous for Se2 (one patient) or compound heterozygous for Se2 and sej (two patients), while the patients in Group A were all homozygous for sej genotypes. Conclusions Even genuinely Le-negative patients, who genetically lack the Le enzyme and theoretically never produce CA19-9, occasionally show a slight increase in serum CA19-9 level when they are homozygous for Se-negative genotypes and suffer from advanced cancer with overproduction of glycans as precursors of CA19-9. Although such cases are not frequent, we should be acquainted with the correlation between serum CA19-9 values and genotypes of Lewis and Secretor genes.