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

BackgroundCancer 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.MethodsSix 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.ResultsAll 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 (t...