Patients with adenocarcinoma had a higher median serum KL-6 level than those with squamous cell carcinoma (519.4 vs. 317.8; p < 0.001) and small cell carcinoma (519.4 vs. 322.4 ; p < 0.001) (Fig. 2d), and patients with advanced-stage disease had a higher median serum KL-6 level than those with early-stage lung cancer (409.1 vs. 321.0; p = 0.007) (Fig. 2e). Here, MUC1 is linked to squamous cell carcinoma.