Elevation of a tumor associated antigen CA 19-9 levels in patients with rheumatic diseases.

We investigated the incidence and characteristics of an elevated tumor associated antigen CA 19-9 in patients with rheumatic diseases. Serum concentration of CA 19-9 was increased in 13 of 39 patients (33.3%) with definite or classical rheumatoid arthritis (RA), in 6 of 19 patients (31.6%) with systemic lupus erythematosus (SLE), in 3 of 9 patients (33.3%) with progressive systemic sclerosis (PSS) and in 9 of the other 35 patients (25.7%). Malignant neoplasm was not detected in any of the patients with rheumatic diseases. Pretreatment of mouse serum with patients' sera did not reduce the measured CA 19-9 values obtained by the conventional assay. The CA 19-9 antigen found in sera from patients with RA was present in a non-IgG fraction, and had the same molecular weight as that in one patient with pancreatic cancer, as determined by gel filtration. These results demonstrated that serum CA 19-9 levels were increased in some patients with rheumatic diseases.