Serum KL-6 levels were measured using a latex agglutination assay, and the levels of tumor markers were determined by chemiluminescent immunoassay.<h4>Results</h4>Serum CYFRA21-1 levels were significantly higher in both the RA-mild ILD and RA-advanced ILD groups compared with the RA-no ILD group (2.10 ng/mL vs. 1.90 ng/mL, <i>q</i> = 0.024; 3.70 ng/mL vs. 1.90 ng/mL, <i>q</i> < 0.001). Here, MUC1 is linked to rheumatoid arthritis.