PDCD1 and breast carcinoma: Indeed, cats showing HER2-positive or TN normal-like mammary carcinoma displayed higher serum PD-1 levels than healthy group (1148.9 pg/mL vs. 534.0 pg/mL, p = 0.017; 3655.1 pg/mL vs. 534.0 pg/mL, p = 0.004, Figure 1A), as well as serum PD-L1 levels (5490.4 pg/mL vs. 1835.5 pg/mL, p = 0.032; 3641.4 pg/mL vs. 1835.5 pg/mL, p = 0.015, Figure 1B).