PDCD1 and breast cancer: In both mixed BC and TNBC subtypes, the natural killer (NK) cell adhesion checkpoint modulator, poliovirus receptor (PVR) gene, scored the highest correlation with RBKO, while LAG3, CTLA4, TIGIT, ICOSLG, CD70, CD274 (PD-L1), CD276 and PDCD1 consistently correlated with RBKO, E2F1, E2F2 signatures and MYC expression as well as with the E2F1 targets: CCNE1, CDK1, TK1 and POLA1. PVR correlated with the RBKO signature with r = 0.3488 (P < 0.0001) and r = 0.4568 (P < 0.0001) in mixed and TNBC BC subtypes, respectively.