Objective  To investigate the expressions of PD-1 and PD-L1 in tissues of Bowen's disease and cutaneous squamous cell carcinoma (cSCC), and analyze their relationships with the tumor differentiation, depth of invasiveness and other clinicopathological characteristics.

  Methods  Skin biopsy specimens of 49 cases of Bowen's disease, 47 cases of highly differentiated cSCC and 25 cases of poorly differentiated cSCC were retrieved, and immunohistochemical stains for PD-1 and PD-L1 in the three groups of samples were performed. Image-pro Plus was used to analyze the average optical density value and data were compared between the three groups.

  Results  Tumor infiltrating cells, instead of tumor cells, expressed PD-1 and PD-L1. The expression levels of PD-1 and PD-L1 were higher in the poorly differentiated cSCC than those in the highly differentiated cSCC (P < 0.001, respectively), and they were also higher in the highly differentiated cSCC than in Bowen's disease (P < 0.01, respectively). PD-L1 expressed significantly higher in deeper cSCC than in superficial cSCC (P < 0.01), while PD-1 showed no significant difference between the two groups(P > 0.05). There was no statistically significant difference in the expressions of PD-1 and PD-L1 in Bowen's disease and cSCC tissues of different genders, ages, races, tumor locations, disease durations and tumor diameters (all P > 0.05).

  Conclusion  The expression of PD-1 and PD-L1 is correlated with the differentiation of cSCC, and the expression of PD-L1 is correlated with the depth of invasiveness of cSCC.