MSLN and lung cancer: Since soluble MSLN in serum samples may also be a potential serum biomarker for malignancies [26], we also found that the MSLN level of the ELC group was higher than that of the HC group, and the MSLN level in the LCBM group was even higher than that of the ELC group, indicating the important significance of MSLN in NSCLC that different threshold expression levels can help to diagnose primary lung cancer and secondary BM and predict the risk of lung cancer BM.