Programmed cell death ligand 1(PD-L1) association in metastatic and non-metastatic oral squamous cell carcinoma: clinicopathologic and immunohistochemical study

Oral Squamous Cell Carcinoma (OSCC) is considered a highly immunosuppressive malignancy largely mediated by the Programmed Cell Death 1/Programmed Cell Death Ligand 1(PD-1/PD-L1) axis. The interaction between PD-L1 expressed on tumor cells and PD-1 receptors on T-cells results in T-cell dysfunction, exhaustion, and immune evasion within the tumor microenvironment. This study aimed to evaluate PD-L1 expression in primary non-metastatic OSCC, primary metastatic OSCC, and nodal metastatic OSCC, as well as to investigate its association with different available clinicopathological parameters. Immunohistochemical staining was performed to retrospectively evaluate PD-L1 expression in 30 archival paraffin-embedded OSCC specimens retrieved from the Department of Oral Pathology, Faculty of Dentistry, and the Oncology Center, Faculty of Medicine, Mansoura University. PD-L1 immunoreactivity was evaluated using a semi-quantitative scoring system based on both the staining intensity and the percentage of positively stained cells. The percentage of immunopositive cells was scored as stated: 0 (0%); 1 (< 25%); 2 (25-50%); 3 (50-75%); and 4 (> 75%). Staining intensity was graded as follows: (0 = negative); (1 = weak); (2 = moderate); and (3 = strong). A combined immunoreactivity score was calculated by adding the percentage and the intensity for each case (range 0-7). The final score was categorized as follows: 0 (negative); 1-3 (weak); 4-7 (strong). Statistical analysis was conducted to determine significant differences and correlations between PD-L1 expression and clinicopathological parameters using the Chi-square test, Monte Carlo test, one-way ANOVA, Student's t-test, and Fisher's exact test. The p-value < 0.05 was considered statistically significant. PD-L1 immunopositivity was detected in all OSCC cases (100%). A statistically significant difference was observed among the different studied groups (p < 0.001), with the strongest PD-L1 expression detected in both primary metastatic and nodal metastatic OSCC. Strong PD-L1 expression showed a significant association with patient age (p = 0.024). Additionally, a significant correlation was identified between PD-L1 expression and the depth of tumor invasion (p < 0.001). PD-L1 expression may have a potential role in tumor progression of OSCC.