Evaluation and limitations of the lipid-associated sialic acid test for the detection of human cancer.

Previous studies and those of the authors have reported about raised levels of lipid-bound sialic acid (LSA) in sera of patients with various neoplasms. Most authors have used the method of Katopodis and Stock for isolating serum LSA. Because of the discrepancy of the amount of extracted LSA with the content of pure gangliosides in sera reported by other groups the authors analyzed the composition of the extracted LSA by immunochemical approaches. They were able to isolate considerable amounts of glycoproteins containing sialic acid as acid alpha-1-glycoprotein, antitrypsin, haptoglobin, antichymotrypsin, and immunoglobulins from the so-called "LSA" fraction. There is a very strong correlation between the raised LSA levels and the content of acid-alpha-1-glycoprotein in the sera of patients with malignancy. Therefore the term lipid-bound sialic acid applied to this test is misleading, since glycoproteins containing sialic acid are mostly responsible for the high "LSA" levels.