We tested the level of sPD-1 in the serum of lung cancer patients, and our results showed that the serum sPD-1 level (87.99 ± 7.568, N = 108) of lung cancer patients was significantly lower than that of the control group (190 ± 17.68, N = 72) (Figure 1A, ***P < 0.0001); no difference was observed of serum sPD-1 in all stages of NSCLC, while downregulation of sPD-1 was found in early-stage NSCLC (82.98 ± 10.43, N = 71) (Figure 1B, ***P < 0.0001). Here, HOXD13 is linked to non-small cell lung carcinoma.