PD-L1 CPS Scoring Accuracy in Small Biopsies and Aspirate Cell Blocks from Patients with Head and Neck Squamous Cell Carcinoma.

To evaluate the performance characteristics of PD-L1 immunohistochemistry (IHC) combined positive scoring (CPS) in core biopsies and aspirate cell blocks from patients with head and neck squamous cell carcinoma (HNSqCCa). PD-L1 IHC using the SP263 antibody was performed on 20 paired cases which consisted of a small biopsy and an excisional specimen. The scores were compared at both the 1% and 20% cutpoints. Using the CPS result obtained from the resected specimen or excisional biopsy as the gold standard, PD-L1 IHC performed on the core biopsy or cell block identified 4 of 6 positive cases (66%) at the 20% cutpoint and 12 of 17 (70%) positive patients at the 1% cutpoint. False positive cases were uncommon at both cutpoints. CPS scoring should be used with caution in small biopsies from patients with HNSqCCa. A negative result should prompt consideration of an excisional biopsy and repeat testing.