CD274 and neoplasm: Despite widespread use of predictive singleplex PD-L1 IHC tests to enrich for likelihood of response to PD-1/PD-L1 axis blockade, the majority of patients do not benefit, and effectiveness is limited in several cancer types likely due to a highly immunosuppressive TME or lack of tumor-specific antigens (Xu-Monette et al., 2017; Hack et al., 2020).