Plenty of studies have demonstrated that miR-155 can act as a sensitive biomarker for monitoring the change in tumor size of breast cancer, more sensitive than canonical biomarkers such as carbohydrate antigen 15-3 (CA15-3), carcinoembryonic antigen (CEA), and tissue polypeptide specific antigen (TPS) [119,120]. This evidence concerns the gene CEACAM5 and breast carcinoma.