CD274 and breast cancer: PD-L1 expression, tumor mutation burden (TMB), TILs, and microsatellite instability (MSI) or mismatch repair deficiency are some of the biomarkers used to predict response to immunotherapy in BC (Qi et al. 2022; Cui et al. 2023; Presti et al. 2022; Carlino et al. 2022).