PGR and breast cancer: We discovered that high mRNA level of HLA-DPB2 was related to estrogen receptor-negative (ER-negative) (Figure 2A1, P < 0.0001), progesterone receptor-negative (Figure 2B1, P < 0.0001), P53-mutated (Figure 2D1, P < 0.0001), high Scarff–Bloom–Richardson (SBR) grade (Figure 2E1, P < 0.0001), and basal-like BC (Figures 2F1–H1, P < 0.0001), and that increased mRNA expression of HLA-DPB1 was associated with ER-negative and basal-like BC (Figure 2A2, P < 0.0001 and Figures 2F2–H2, P < 0.05).