CEACAM5 and breast cancer: ROC analysis identified optimal cut-off values (Youden index) for predicting PET positivity, with 19.25 U/mL for CA 15-3 (sensitivity 70.1%, specificity 90.4%, LR + 7.38, AUC 0.837), 3.15 ng/mL for CEA (sensitivity 65.6%, specificity 85.2%, LR + 4.43, AUC 0.821), and 13.5 U/mL for CA 125 (sensitivity 65.6%, specificity 62.9%, LR + 1.77, AUC 0.664), indicating that CA 15–3 and CEA in particular may serve as complementary tools for PET imaging and assessing skeletal metastatic burden in breast cancer.