Regarding the serum PD-L1 levels, the optimal cut-off value in cats with HER2-positive mammary carcinoma was 2545.0 pg/mL (AUC = 0.778 ± 0.117, 95% CI: 0.548–1.000, p = 0.030; sensitivity = 66.7%; specificity = 92.3%; Figure 1E) and 2519.0 pg/mL in cats with TN normal-like tumor subtype (AUC = 0.857 ± 0.123, 95% CI: 0.617–1.000, p = 0.010; sensitivity = 85.7%; specificity = 92.3%; Figure 1F). This evidence concerns the gene CD274 and breast carcinoma.