PDCD1 and breast cancer: The results showed that immune checkpoints SIGLEC15 (p = 1.17 × 10−27), LAG3 (p = 7.38 × 10−16), PDCD1 (p = 2.19 × 10−10), CTLA4 (p = 1.33 × 10−17), TIGIT (p = 4.76 × 10−13), CD274 (p = 1.10 × 10−5), and PDCD1LG2 (p = 7.19 × 10−11) were expressed at lower levels in ER+ BC than in ER− BC (see Figure 5(b)).