PDCD1 and breast cancer: In the setting of immunotherapy programmed cell death protein 1 (PD-1)/programmed cell death 1 ligand 1 (PD-L1), tumor mutational burden (TMB) and tumor-infiltrating lymphocytes (TILs) are dependable (though not ideal) biomarkers in various tumor entities to predict the success of immune checkpoint inhibition, but potential value in breast cancer is so far limited to early TNBC and data are still regarded as immature (Teng et al., 2015; Goodman et al., 2017).