ERBB2 and breast cancer: The ROC curve analysis demonstrated that in M0 patients, serum miR-19a levels could differentiate patients with HER2− (AUC  = 0.814; p = 0.0001) and HER2+ (AUC  = 0.774; p = 0.004) breast cancer from HDs; whereas serum miR-21 levels could distinguish patients with HER2+ from patients with HER2− breast cancer (AUC  = 0.707; p = 0.042) and HDs (AUC  = 0.812; p = 0.001) (Figure S3).