CD274 and neoplasm: In the phase 1b KEYNOTE-012 study of pembrolizumab in PD-L1+ TNBC (n = 27 evaluable patients), PD-L1 positivity was defined as expression in the stroma or in ≥ 1% of tumor cells based on IHC staining using the 22C3 PD-L1 antibody.