MUC1 and cancer: It has been reported that KL‐6 has increased expression in various malignant tumors, can be used as a potential biomarker for tumors, and is of great value in the diagnosis, treatment, and monitoring of tumors.20 However, in this study, the serum KL‐6 level in patients with lung cancer was not significantly increased compared with that in healthy individuals, probably because KL‐6 was not adequately specific in lung cancer, and in clinical practice, the sensitivity and specificity should be improved by combining it with other tumor markers.