MUC1 and rheumatoid arthritis: When we stratified by the type of underlying CTD, including patients with RA [mean (SD) 563.9 (627.0) vs. 231.3 (188.5) U/mL, p < 0.001], SSc [766.4 (754.6) vs. 224.0 (188.5) U/mL, p = 0.002], IM [808.1 (746.9) vs. 291.4 (238.6) U/mL, p < 0.001], and others (SS or SLE) [884.9 (762.3) vs. 225.7 (107.0), p < 0.001], significantly higher serum KL-6 values were observed in patients with ILD than in patients without ILD (Fig. 1).