CEACAM6 and metastasis: In order to further analyze the level of CEACAM6 in metastatic LUAD patients, we divided stage IV patients into 3 subgroups including leptomeningeal metastasis (LM, male: 50.0%, median age of 57.5 years with IQR of 54.3–61.8 years), brain metastasis (BM, male: 40.0%, median age of 55.5 years with IQR of 50.5–66.5 years) and other organ metastasis (OM, male: 44.4%, median age of 65.5 years with IQR of 54.3–69.5 years).