Relationship of total serum sialic acid to sialylglycoprotein acute-phase reactants in malignant melanoma.

Reported elevations of total serum sialic acid may be a result of shed tumour-related membrane sialyglycoprotein and/or concurrent elevation of non-specific, acute-phase reactant sialoglycoprotein. To clarify further the specificity and sensitivity of serum sialic acid monitoring, analyses of sialic acid by the thiobarbituric acid method and acute-phase reactants by radial immunodiffusion were made using the same malignant melanoma patients' sera. Preliminary studies of IgG, IgA, IgM, ceruloplasmin and C-reactive protein suggested that these would not be valuable monitors of tumour burden. Single serum samples from 59 melanoma patients and age- and sex-matched controls were further examined for sialic acid, alpha 1-acid glycoprotein, alpha 1-antitrypsin, haptoglobin, and alpha 2-macroglobulin. Patients were grouped according to tumour burden. In pairwise statistical tests, differences between groups tended to be greater for sialic acid than for acute-phase reactants. On discriminant analysis , sialic acid was clearly the most significant single discriminator between groups, with an F statistic of P < 0.00005. Although alpha 1-acid glycoprotein was quite strongly correlated with sialic acid, it was not such a good discriminator and did not add significantly to the predictive power of sialic acid alone.