ERBB2 and breast carcinoma: Furthermore, the optimal cut-off value of serum PD-1 levels was 801.6 pg/mL in cats with HER2-positive mammary carcinoma (AUC = 0.765 ± 0.104, 95% CI: 0.562–0.968, p = 0.031; sensitivity = 54.5%; specificity = 91.7%; Figure 1C) and 801.6 pg/mL in cats with TN normal-like mammary carcinoma (AUC = 0.857 ± 0.092, 95% CI: 0.676–1.000, p = 0.011; sensitivity = 57.1%; specificity = 91.7%; Figure 1D).