Programmed Death Ligand-1 Combined Positive Score Concordance and Interrater Reliability in Primary Tumors and Synchronous Lymph Node Metastases in Resected Cases of p16⁺ Oropharyngeal Squamous Cell Carcinoma

Context.—Pembrolizumab is used in patients with metastatic head and neck squamous cell carcinoma contingent upon the programmed death ligand-1 (PD-L1) combined positive score (CPS). Objective.—To compare PD-L1 CPS scores derived from paired resected primary tumors (PTs) and lymph node metastases (LMs) in patients with p16^þ oropharyngeal squamous cell carcinoma (OPSCC). Design.—We identified 38 resected p16^þ OPSCCs for which paired PTs and LMs were available. PD-L1 immunohistochemistry using the SP263 antibody clone was done on both the PT and the LM. CPS scoring was performed by 4 observers, and data were analyzed at the CPS cut points of greater than or equal to 1 and 20 in regard to interobserver and interspecimen agreement. Results.—Overall agreement between consensus CPS scoring of PT and LM was seen in 76% of paired specimens (j ¼ 0.53). No specimen received a negative consensus score. Interobserver agreement for both PT and LM was fair to substantial (j ¼ 0.54 and 0.51, respectively) and was inferior to that seen in a prospective series of unselected head and neck squamous carcinoma cases evaluated at our institution (j ¼ 0.84). Conclusions.—Given the high rates of interobserver and interspecimen variability, evaluation of additional material or by additional observers may be of value in performing CPS scoring in cases of p16^þ OPSCC. This is particularly the case when a negative or low-positive result is being evaluated in a patient who is otherwise a good candidate for immunotherapy.