MUC1 and cancer: For patients with lung cancer and ILD, serum KL-6 levels >500 U/mL is more likely to indicate the severity and activity of the underlying fibrotic lung disease rather than providing independent prognostic information about the cancer itself, further investigation is still required to validate that whether KL-6 is a cancer-specific predictive biomarker for these population and what is an optimal cut-off value.