CD274 and head and neck squamous cell carcinoma: PD-L1 IHC 22C3 pharmDx is also clinically validated and approved by the FDA in selecting patients for pembrolizumab monotherapy or combination therapies who have non–small cell lung cancer (NSCLC; determined using tumor proportion score [TPS]), head and neck squamous cell carcinoma (HNSCC), esophageal squamous cell carcinoma (ESCC), and triple-negative breast cancer (TNBC) [3, 8].