Abstract: Objective · To investigate the relationship between of programmed cell death 1 ligand 2 (PD-L2) in colorectal cancer and prognosis, and explore the feasibility of application of PD-L2 in confocal laser endomicroscopy in the diagnosis of colorectal cancer. Methods · Immunohistochemistry was used to detect the of PD-L2 in 100 patients with colorectal cancer. The relationship between the levels and the prognosis of patients was analyzed. The s of PD-L2 in 30 cases of early colorectal cancer and adjacent normal mucosa were detectedimmunohistochemistry and Western blotting. Confocal laser endomicroscopy was used to observe the difference in fluorescence intensity between early colorectal cancer and adjacent normal mucosa after being incubated with PD-L2 fluorescent antibody. Results · There were statistically significant differences in T-stage and distant metastasis between the patients with low and high of PD-L2, and they were both positively correlated with of PD-L2 (r0.274, P0.009; r0.216, P0.039). There was also a positive correlation between PD-L2 membrane and T stage (r0.201, P0.037). Survival analysis showed that the survival rate of patients with high PD-L2 was significantly lower than that of patients with low PD-L2 (P0.000). The protein of PD-L2 in early colorectal cancer was significantly higher than that in adjacent normal mucosa. Under confocal laser endomicroscopy, the fluorescence intensity of early colorectal cancer was higher than that of adjacent normal mucosa. Conclusion · High of PD-L2 in colorectal cancer predicts poor prognosis in patients. Application of PD-L2 in confocal laser endomicroscopy may contribute to the diagnosis of colorectal cancer.

Key words: programmed cell death 1 ligand 2, confocal laser endomicroscopy, colorectal cancer, diagnosis