Moreover, since immunotherapy is an emerging treatment option for BC, we then conducted mRNA-level expression difference analysis of PD-1 and PD-L1, the most common immune checkpoints of BC, in two clusters and found a higher level of PD-1 in cluster 2 (p < 0.001), implying that immunotherapy is available to patients in this cluster (Figure 3D). This evidence concerns the gene CD274 and breast cancer.