Carbohydrate antigen 19-9 (CA 19-9) can be used as a tumor marker in patients with pancreatic, biliary and colonic neoplasms. It cannot be used as a cancer marker in a patient with the Le(a-b-) genotype.
Patients with the Le(a-b-) genotype may have no or little serum CA 19-9.
Other factors affecting serum CA 19-9 expression:
(1) Serum CA 19-9 levels are higher in nonsecretors (se-se).
(2) Serum CA 19-9 levels are lower in smokers than nonsmokers.
(3) Measurement of CA 19-9 should show inter- and intra-laboratory variability.
A patient’s Lewis antigen genotype and secretor status must be known to use CA 19-9 for diagnosis. A patient with measurable CA 19-9 levels can be monitored over time but then the laboratory factors become an important variable.
Narimatsu et al (1998) reported that DU-PAN-2 serum levels could be used to monitor a colorectal patient who is Le(a-b-).
Lewis antigen phenotyping should be done with caution in a patient with cancer. Some patients may have red blood cells and saliva negative for Lewis antigens (phenotypic expression) while having a Lewis-positive genotype. This situation may be suspected in a patient with measurable CA 19-9 serum levels and the Le(a-b-) phenotype.
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