Immunohistochemical evaluation of PD-1 and PD-L1 in oral squamous cell carcinoma and oral epithelial dysplasia

Background and Objectives: Oral squamous cell carcinoma (OSCC) is one of the most common cancers globally, accounting for a significant portion of head and neck malignancies. Most cases are preceded by oral potentially malignant disorders (OPMD), which may progress through histological changes such as hyperplasia, hyperkeratosis, and oral epithelial dysplasia (OED). A key factor in this progression is immune evasion, particularly through the PD-1/PD-L1 pathway, which tumour cells exploit to escape immune surveillance. Although therapeutic strategies targeting PD-1/PD-L1 are promising, their expression patterns and prognostic significance in OED and OSCC remain underexplored. This study aimed to evaluate and compare the immunohistochemical expression of PD-1 and PD-L1 in OED and OSCC, including their different grades. Methods: An analytical cross-sectional study was conducted with 66 samples (33 each of OED and OSCC). Diagnoses were confirmed histopathologically. Samples were stained using immunohistochemistry for PD-1 and PD-L1, and expression was assessed using the immunoreactivity score (IRS). Statistical analysis was performed using SPSS version 20. Results and Discussion: PD-1 and PD-L1 expression were significantly higher in OSCC compared with OED ( P < 0.001). Expression levels increased progressively with higher grades of dysplasia and poorer tumour differentiation. A positive correlation between PD-1 and PD-L1 expression was observed within both groups, aligning with previous studies. Conclusion: These findings highlight the potential role of the PD-1/PD-L1 axis in early tumour development and immune evasion. Further research with larger sample sizes and clinical correlation could establish PD-1/PD-L1 as targets for immunotherapy, potentially improving outcomes in advanced OSCC and severe dysplasia.