Serum KL-6 levels were significantly higher in patients with CFIP (n = 19; 1581 (304–8298) U•mL−1, p < 0.0001), UCTD-ILD (n = 16; 1045 (363–4560) U•mL−1, p = 0.0494), and CTD-ILD (n = 33; 1117 (289–3943) U•mL−1, p = 0.0069) than in control subjects (n = 26; 261 (140–491) U•mL−1). The gene discussed is MUC1; the disease is interstitial lung disease.