Determining PD-L1 expression in head and neck squamous cell carcinoma using immunohistochemistry.

Advanced head and neck squamous cell carcinoma (HNSCC) has limited treatment options. Programmed death-ligand1 (PD-L1) expressed by tumor cells interacts with PD-1 receptor on T lymphocytes leading to immune evasive response and survival advantage. Therapy with immune check-point inhibitors target PD-1/PD-L1 blockade inducing tumor regression. Immunohistochemistry (IHC) for PD-L1 expression enables patient selection for immunotherapy and may be considered a potential predictor of clinical response.A retrospective analysis of IHC for PD-L1 expression using manual laboratory developed technique (LDT) with antibody clone 22C3 (Dako) in 93 cases of HNSCC. PD-L1 expression was correlated with age, gender, tumor site, grade and stage.PD-L1 IHC was performed in 93 cases and immunopositivity was noted in 59 (63.4%) cases. High expression with combined proportion score (CPS) =50 was seen in 15 (16.1%) cases and low expression with CPS =1 expression was seen in 44 (47.3%) cases. An almost-perfect interobserver agreement was noted by two pathologists for PD-L1 IHC expression (Cohen's kappa coefficient = 0.910). No statistically significant correlation was noted between PD-L1 score and patient demographics, tumor site, grade or stage.Detection of PD-L1 status by IHC enables identification of HNSCC patients eligible for future targeted immunotherapy.