Originally described as a marker for colorectal cancer,1 CA 19-9 has become the gold standard serologic marker for pancreatic cancer, with reported sensitivity and specificity as high as 87% and 98%, respectively.2 However, known limitations of CA19-9 as a biomarker include the following: (1) elevation of CA 19-9 levels with hyperbilirubinemia of both malignant and benign causes; and (2) falsely low CA 19-9 levels in individuals with the Le(a−b−) blood group who do not synthesize CA 19-9 despite having advanced pancreatic cancer. Because the CA 19-9 antigen is also a sialylated Lea blood group antigen,3 individuals with the Le(a−b−) blood group are deficient in a fucosyltransferase specified by the Le gene that is involved in the synthesis of the CA 19-9 antigen. About 5% to 14% of the population genotypically have the Le(a−b−) blood group and thus are unable to synthesize CA 19-9.4 In an attempt to improve the diagnostic accuracy of CA 19-9, the study by Ćwik and colleagues evaluates the combination of CA 19-9 and CA 125, which is a serum marker that is often used to diagnose ovarian cancer.
Hwang R, Evans D. Cancer Antigens 19-9 and 125 in the Differential Diagnosis of Pancreatic Mass Lesions—Invited Critique. Arch Surg. 2006;141(10):974. doi:10.1001/archsurg.141.10.974