The serum levels of ProGrp, CA211, and NSE of patients in the small-cell lung cancer observation group were significantly higher than those in the squamous carcinoma and adenocarcinoma groups, and the serum levels of patients with stage I and II lung cancer were significantly lower than those of patients with stage III and IV, with statistically significant differences (P > 0.05), see Figure 1. Here, ENO2 is linked to squamous cell carcinoma.