MUC1 and idiopathic pulmonary fibrosis: It was shown here that (1) the serum level of KL-6/MUC1 was maintained within the normal range in dissociation with the SP-D level, which was elevated in asymptomatic patients with honeycombing on HRCT, (2) these patients with high SP-D but low KL-6 in their serum exhibited prolonged survival, (3) there are obvious differences in the distribution patterns between SP-D and KL-6/MUC1 in the IPF lung, especially in the clearance route, which may cause the observed dissociation between these biomarkers.