Among patients with lung cancer, the median serum KL-6 levels were significantly higher in categories 1 and 2 (combined) than in category 3 (492.2 vs. 333.0; p = 0.019) (Fig. 2a), higher in patients with underlying ILD than in those without ILD (821.3 vs. 335.8; p < 0.001) (Fig. 2b), and lower in patients with better Eastern Cooperative Oncology Group (ECOG) performance status (PS) scores (0 to 1) than in those with worse scores (2 to 4) (330.7 vs. 506.8; p < 0.001) (Fig. 2c). Here, MUC1 is linked to interstitial lung disease.