Sokai et al. showed that the absolute changes in serum KL-6 level over 6 months were significantly correlated with the absolute changes in FVC and DLco over 6 months (r = − 0.38, p < 0.01; r = − 0.33, p < 0.01, respectively) among 75 patents with IPF, 14.7% of whom received pirfenidone [20]. Here, MUC1 is linked to idiopathic pulmonary fibrosis.